[baronfel]

Fixes #12002

This writes the Compilation Metadata References and Compilation Options tables to the CustomDebugInformation area of the PDB. There are a number of TODOs, and I'm not 100% sure I'm getting the actual information we will want to get a real end-to-end setup.

With these changes, we look like other .NET assemblies!

What this should do immediately is allow VS-based tooling to synthesize MetadataReferences from this cached data, so that go-to-def for sourcelinked files has a matching set of assembly references to do typechecking against (and therefore light up IDE tooling).

There are a number of TODOs that I'd like to get some feedback on. I'm fairly sure I'm reading required data correctly, but I want to make sure the sources I'm pulling it from are correct.
Also I'm certain I'm missing a number of compiler options that would be necessary to have on the read-side of this to ensure 1:1 compilation.
Finally, I haven't done the step that would map from the compilation options + compilation references to a proper FSharpProjectOptions - that would probably need to be done to show a true end-to-end in an editor.

I would love any and all review/pointers for the next steps here.

[vzarytovskii]

Test framework will probably also need to be extended, to check those:

fsharp/tests/FSharp.Test.Utilities/Compiler.fs

Lines 1210 to 1215 in 3d4eb5c

	let verifyPdb (options: PdbVerificationOption list) (result: CompilationResult) : CompilationResult =
	match result with
	| CompilationResult.Success r -> verifyPortablePdb r options
	| _ -> failwith "Result should be \"Success\" in order to verify PDB."
	result

Example for sequence points:

fsharp/tests/FSharp.Test.Utilities/Compiler.fs

Lines 1151 to 1161 in 3d4eb5c

	let private verifySequencePoints (reader: MetadataReader) expectedSequencePoints =
	let sequencePoints =
	[ for sp in reader.MethodDebugInformation do
	let mdi = reader.GetMethodDebugInformation sp
	yield! mdi.GetSequencePoints() ]
	|> List.sortBy (fun sp -> sp.StartLine)
	|> List.map (fun sp -> (Line sp.StartLine, Col sp.StartColumn, Line sp.EndLine, Col sp.EndColumn) )
	if sequencePoints <> expectedSequencePoints then
	failwith $"Expected sequence points are different from PDB.\nExpected: %A{expectedSequencePoints}\nActual: %A{sequencePoints}"

And import tables:

fsharp/tests/FSharp.Test.Utilities/Compiler.fs

Lines 1117 to 1149 in 3d4eb5c

	let private verifyPdbImportTables (reader: MetadataReader) (scopes: ImportScope list list) =
	// There always should be 2 import scopes - 1 empty "root" one, and one flattened table of imports for current scope.
	if reader.ImportScopes.Count < 2 then
	failwith $"Expected to have at least 2 import scopes, but found {reader.ImportScopes.Count}."
	// Sanity check: explicitly test that first import scope is indeed an apty one (i.e. there are no imports).
	let rootScope = reader.ImportScopes.ToImmutableArray().Item(0) |> reader.GetImportScope
	let rootScopeImportsLength = rootScope.GetImports().ToImmutableArray().Length
	if rootScopeImportsLength <> 0 then
	failwith $"Expected root scope to have 0 imports, but got {rootScopeImportsLength}."
	let pdbScopes = [ for import in reader.ImportScopes -> reader.GetImportScope import ] |> List.skip 1 |> List.rev
	if pdbScopes.Length <> scopes.Length then
	failwith $"Expected import scopes amount is {scopes.Length}, but got {pdbScopes.Length}."
	for (pdbScope, expectedScope) in List.zip pdbScopes scopes do
	let imports = [ for import in pdbScope.GetImports() ->
	match import.Kind with
	| ImportDefinitionKind.ImportNamespace ->
	let targetNamespaceBlob = import.TargetNamespace
	let targetNamespaceBytes = reader.GetBlobBytes(targetNamespaceBlob)
	let name = Encoding.UTF8.GetString(targetNamespaceBytes, 0, targetNamespaceBytes.Length)
	Some { Kind = import.Kind; Name = name }
	| _ -> None ] |> List.filter Option.isSome |> List.map Option.get
	if expectedScope.Length <> imports.Length then
	failwith $"Expected imports amount is {expectedScope.Length}, but got {imports.Length}\nExpected:\n%A{expectedScope}\nActual:%A{imports}"
	if expectedScope <> imports then
	failwith $"Expected imports are different from PDB.\nExpected:\n%A{expectedScope}\nActual:%A{imports}"