Use managed PPDB readers for MonoVM

[marek-safar]

We should investigate dropping ppdb reader support from MonoVM for easier size saving for some workloads. If I remember correctly the biggest price comes from compresses ppdb support and we could just make ppdb functionality coupled with debug mode support and let the linker to remove it for anything else.

The relevant code which would need to be adopted to MonoVM starts at

runtime/src/coreclr/src/System.Private.CoreLib/src/System/Diagnostics/StackFrameHelper.cs

Line 93 in 7493302

internal void InitializeSourceInfo(int iSkip, bool fNeedFileInfo, Exception? exception)

@thaystg @lambdageek @vargaz

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[lambdageek]

So the complication is that mini (JIT, AOT, and AOT LLVM) uses PDBs to decide where to place sequence points. I'm not sure how complicated the bootstrapping will look like if the JIT needs to call managed code to read a PDB. So the alternative is to add a new codegen mode with automatically chosen sequence point locations.

I'm surprised that native PPDB support needs a lot of code in the runtime - since PPDBs are just CIL images with some new tables, a lot of the code is shared with normal metadata reading. We do have to bundle in some compression code, but I think it's fairly compact.

/cc @vargaz

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