Use reflection to get source location when FCS doesn't give enough information

[dungpa]

Partial fix for #947 (NOT YET READY).

For Octokit NuGet package, FCS returns faulty ranges (no range or a dummy range with wrong information). We try to use Reflection to recover source locations. I'm not sure it's a good approach; any other idea is appreciated.

@ctaggart It seems pdbReader.GetMethod doesn't work correctly for any overriden/abstract member e.g. any symbol from this line:

let a = github.Activity.Events.GetAll()

Is this a SourceLink's bug? Any idea?

[dungpa]

@ctaggart I need your help with this one to move forward. Should I wait for changes in SourceLink or discard this PR as we don't support source-indexed C# assemblies at this point?

[ctaggart]

As I just mentioned in ctaggart/SourceLink#63, not all files or methods gets indexed by the compilers. F12 at design time will only work with concrete methods that get source indexed, not any of the interfaces.

[dungpa]

That sounds really limiting. On a related note, can signature files (*.fsi) be source indexed?

[dungpa]

Closing this PR until there is more versatile support for pdb files from SourceLink.

[ctaggart]

I believe Portable PDBs ctaggart/SourceLink#93 will solve several of the issues. I'll create a new issue in this repo.