Transparent Compiler: Fails when signature file is not exactly next to source file

[TheAngryByrd]

Please provide a succinct description of the issue.

Repro steps

Provide the steps required to reproduce the problem:

1. Create a project with multiple files that don't depend on each other
2. Use a wildcard to add all the files. see fsautocomplete

Expected behavior

Typechecking completes

Actual behavior

Type checking fails with "Oops!!" exception

Known workarounds

Comment out

fsharp/src/Compiler/Service/TransparentCompiler.fs

Lines 1418 to 1422 in f68d7b6

	if
	tcInfo.stateContainsNodes
	|> Set.contains (NodeToTypeCheck.PhysicalFile(index + 1))
	then
	failwith $"Oops!!!"

Related information

Provide any related information (optional):

• Operating system
• .NET Runtime kind (.NET Core, .NET Framework, Mono)
• Editing Tools (e.g. Visual Studio Version, Visual Studio)

[vzarytovskii]

Yeah, it's fine to remove/comment it as we do with physical file. Feel free to do it in PR.

[majocha]

The same false assumption that signature must immediately precede implementation exists in IncrementalBuild. It does not throw, but I think it may lead to needless type checks.