Share unified UTF-8/16 parsing with BigInteger

[huoyaoyuan]

Follow up of #85978 . Should really be in same PR.

Copied latest CoreLib implementation and polyfill internal interfaces.
This allows sharing UTF unified parsing and formatting code.

Originally I tried this with heavy ifdefs and tricks like using TChar = System.Char;. Then I realized that all the internal members can be polyfilled in S.R.Numerics, with very little overhead for UTF-16. This also unblocks UTF-8 adoption for BigInteger.

Wanna check with @stephentoub for whether this design is desired.

[ghost]

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Issue Details

---

Follow up of #85978 . Should really be in same PR.

Copied latest CoreLib implementation and polyfill internal interfaces.
This allows sharing UTF unified parsing and formatting code.

Originally I tried this with heavy ifdefs and tricks like using TChar = System.Char;. Then I realized that all the internal members can be polyfilled in S.R.Numerics, with very little overhead for UTF-16. This also unblocks UTF-8 adoption for BigInteger.

Wanna check with @stephentoub for whether this design is desired.

Author:	huoyaoyuan
Assignees:	-
Labels:	area-System.Numerics, community-contribution
Milestone:	-

[huoyaoyuan]

Test failures look unrelated. No integer/biginteger related.

[tannergooding]

CC. @vargaz, another LLVM OOM. It's not clear to me which line indicates the failing assembly so I can know what needs to be skipped until the final PR can get merged?

C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : Failed to compile C:\helix\work\workitem\e\wasm_build\obj\wasm\for-build\aot-instances.dll.bc -> C:\helix\work\workitem\e\wasm_build\obj\wasm\for-build\aot-instances.dll.o [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : C:\helix\work\workitem\e\publish>C:\Windows\System32\chcp.com 65001 1>nul [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : C:\helix\work\workitem\e\publish>setlocal [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : C:\helix\work\workitem\e\publish>set errorlevel=dummy [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : C:\helix\work\workitem\e\publish>set errorlevel= [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : C:\helix\work\workitem\e\publish>"C:\helix\work\correlation\build\\wasi-sdk\\bin\clang.exe" "@C:\helix\work\correlation\build\microsoft.netcore.app.runtime.wasi-wasm\runtimes\wasi-wasm\native\src\wasi-default.rsp" "@C:\helix\work\workitem\e\wasm_build\obj\wasm\for-build\wasi-compile-bc.rsp" -c -o "C:\Users\ContainerAdministrator\AppData\Local\Temp\tmpa2qi3t.tmp" "C:\helix\work\workitem\e\wasm_build\obj\wasm\for-build\aot-instances.dll.bc" [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : clang version 16.0.0 [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : Target: wasm32-unknown-wasi [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : Thread model: posix [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : InstalledDir: C:/helix/work/correlation/build//wasi-sdk//bin [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : (in-process) [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : "C:/helix/work/correlation/build/wasi-sdk/bin/clang.exe" -cc1 -triple wasm32-unknown-wasi -emit-obj -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name aot-instances.dll.bc -mrelocation-model static -mframe-pointer=none -ffp-contract=on -fno-rounding-math -mconstructor-aliases -target-cpu generic -fvisibility=hidden -mllvm -treat-scalable-fixed-error-as-warning -debug-info-kind=constructor -dwarf-version=4 -debugger-tuning=gdb -v -fcoverage-compilation-dir=C:/helix/work/workitem/e/publish -resource-dir C:/helix/work/correlation/build/wasi-sdk/lib/clang/16 -Oz -fdebug-compilation-dir=C:/helix/work/workitem/e/publish -ferror-limit 19 -fgnuc-version=4.2.1 -vectorize-slp -o "C:\\Users\\ContainerAdministrator\\AppData\\Local\\Temp\\tmpa2qi3t.tmp" -x ir "C:\\helix\\work\\workitem\\e\\wasm_build\\obj\\wasm\\for-build\\aot-instances.dll.bc" [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : clang -cc1 version 16.0.0 based upon LLVM 16.0.0 default target wasm32-wasi [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : LLVM ERROR: out of memory [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : Allocation failed [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script. [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : Stack dump: [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : 0.	Program arguments: C:\\helix\\work\\correlation\\build\\\\wasi-sdk\\\\bin\\clang.exe @C:\\helix\\work\\correlation\\build\\microsoft.netcore.app.runtime.wasi-wasm\\runtimes\\wasi-wasm\\native\\src\\wasi-default.rsp @C:\\helix\\work\\workitem\\e\\wasm_build\\obj\\wasm\\for-build\\wasi-compile-bc.rsp -c -o C:\\Users\\ContainerAdministrator\\AppData\\Local\\Temp\\tmpa2qi3t.tmp C:\\helix\\work\\workitem\\e\\wasm_build\\obj\\wasm\\for-build\\aot-instances.dll.bc [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : 1.	Code generation [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : 2.	Running pass 'Function Pass Manager' on module 'C:\helix\work\workitem\e\wasm_build\obj\wasm\for-build\aot-instances.dll.bc'. [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]
C:\helix\work\correlation\build\wasm-shared\WasmApp.Common.targets(818,5): error : 3.	Running pass 'WebAssembly Instruction Selection' on function '@aot_instances_System_SZGenericArrayEnumerator_1_T_SINGLE__cctor' [C:\helix\work\workitem\e\publish\ProxyProjectForAOTOnHelix.proj]

[vargaz]

Those failures are happening on other PRs as well, so i think this is ok to merge.