gh-127503: Improve tracebacks on Emscripten when there is a trap

[hoodmane]

This PR solves two problems:

1. No Python traceback shown on segfault/trap
2. The JavaScript source line is shown

The JavaScript source line is super long and completely unenlightening, whereas the Python traceback is very helpful.

• Issue: Emscripten: Make python.sh function as proper Python CLI #127503

[hoodmane]

After this change a trap in the test suite looks as follows:

Details

Aborted(Assertion failed: callable != NULL, at: ../../../../Include/internal/pycore_call.h,116,_PyVectorcall_FunctionInline)
RuntimeError: Aborted(Assertion failed: callable != NULL, at: ../../../../Include/internal/pycore_call.h,116,_PyVectorcall_FunctionInline). Build with -sASSERTIONS for more info.
at abort (file:///home/rchatham/cpython/cross-build/wasm32-emscripten/build/python/python.mjs:261:15)
at ___assert_fail (file:///home/rchatham/cpython/cross-build/wasm32-emscripten/build/python/python.mjs:1735:7)
at wasm://wasm/02f678e6:wasm-function[787]:0x1c26ed
at wasm://wasm/02f678e6:wasm-function[798]:0x1c35ad
at wasm://wasm/02f678e6:wasm-function[3560]:0x3575f2
at wasm://wasm/02f678e6:wasm-function[3558]:0x30d1f8
at wasm://wasm/02f678e6:wasm-function[3557]:0x30cfca
at wasm://wasm/02f678e6:wasm-function[3519]:0x3084d2
at wasm://wasm/02f678e6:wasm-function[3560]:0x318045
at wasm://wasm/02f678e6:wasm-function[3558]:0x30d1f8
Stack (most recent call first):
File "<frozen __hello__>", line 0 in <module>
File "<frozen importlib._bootstrap>", line 1176 in exec_module
File "<frozen importlib._bootstrap>", line 935 in _load_unlocked
File "<frozen importlib._bootstrap>", line 1339 in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 1368 in _find_and_load
File "/home/rchatham/cpython/Lib/importlib/util.py", line 90 in find_spec
File "/home/rchatham/cpython/Lib/test/test_ctypes/test_values.py", line 85 in test_frozentable
File "/home/rchatham/cpython/Lib/unittest/case.py", line 606 in _callTestMethod
File "/home/rchatham/cpython/Lib/unittest/case.py", line 660 in run
File "/home/rchatham/cpython/Lib/unittest/case.py", line 716 in __call__
File "/home/rchatham/cpython/Lib/unittest/suite.py", line 122 in run
File "/home/rchatham/cpython/Lib/unittest/suite.py", line 84 in __call__
File "/home/rchatham/cpython/Lib/unittest/suite.py", line 122 in run
File "/home/rchatham/cpython/Lib/unittest/suite.py", line 84 in __call__
File "/home/rchatham/cpython/Lib/unittest/suite.py", line 122 in run
File "/home/rchatham/cpython/Lib/unittest/suite.py", line 84 in __call__
File "/home/rchatham/cpython/Lib/unittest/suite.py", line 122 in run
File "/home/rchatham/cpython/Lib/unittest/suite.py", line 84 in __call__
File "/home/rchatham/cpython/Lib/test/libregrtest/testresult.py", line 148 in run
File "/home/rchatham/cpython/Lib/test/libregrtest/single.py", line 84 in _run_suite
File "/home/rchatham/cpython/Lib/test/libregrtest/single.py", line 42 in run_unittest
File "/home/rchatham/cpython/Lib/test/libregrtest/single.py", line 162 in test_func
File "/home/rchatham/cpython/Lib/test/libregrtest/single.py", line 118 in regrtest_runner
File "/home/rchatham/cpython/Lib/test/libregrtest/single.py", line 165 in _load_run_test
File "/home/rchatham/cpython/Lib/test/libregrtest/single.py", line 210 in _runtest_env_changed_exc
File "/home/rchatham/cpython/Lib/test/libregrtest/single.py", line 319 in _runtest
File "/home/rchatham/cpython/Lib/test/libregrtest/single.py", line 348 in run_single_test
File "/home/rchatham/cpython/Lib/test/libregrtest/main.py", line 378 in run_test
File "/home/rchatham/cpython/Lib/test/libregrtest/main.py", line 408 in run_tests_sequentially
File "/home/rchatham/cpython/Lib/test/libregrtest/main.py", line 550 in _run_tests
File "/home/rchatham/cpython/Lib/test/libregrtest/main.py", line 585 in run_tests
File "/home/rchatham/cpython/Lib/test/libregrtest/main.py", line 757 in main
File "/home/rchatham/cpython/Lib/test/libregrtest/main.py", line 765 in main
File "/home/rchatham/cpython/Lib/test/__main__.py", line 2 in <module>
File "/home/rchatham/cpython/Lib/runpy.py", line 88 in _run_code
File "/home/rchatham/cpython/Lib/runpy.py", line 198 in _run_module_as_main

[freakboy3742]

Definitely a nicer stack track than the previous behaviour 👍