Create and publish missing symbols

[directhex]

We have four classes of symbols missing at VS insertion, according to validation:

• tasks - we were producing ppdb's but not packaging them in the .symbols.nuget, this PR addresses that
• wasm tasks - we are already producing and shipping ppdb's, implies an issue with ppdb->pdb conversion affecting insertion
• mono-aot-cross.exe - we were not producing pdb's, this PR addresses that
• llvm (llc and opt) - we need to get the pdb's from the llvm-project repo build (if indeed we produce them) into this one

Submitting a PR to see if my changes broke the build.

[ghost]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[directhex]

There are still some gaps in this, but it should definitely improve matters.

Private build: https://dev.azure.com/dnceng/internal/_build/results?buildId=1361044&view=results

[directhex]

/backport to release/6.0

[github-actions]

Started backporting to release/6.0: https://github.com/dotnet/runtime/actions/runs/1238541724

[steveisok]

/backport to release/6.0-rc2

[github-actions]

Started backporting to release/6.0-rc2: https://github.com/dotnet/runtime/actions/runs/1245529991