[DRAFT] Add Roslyn lookup based on metadata

[Emptycz]

This is my very first open-source contribution, so I apologise for any mistakes with this PR or my approach to contributing!

This is still in draft (there is a lot of missing parts -- see the Issues todo-list below)

Overview:

This PR should add the generation of temporary files based on metadata. The goal is to have "jump to definition" (ctrl + click) feature not only for in-solution classes/methods (that's already implemented), but also for built-in methods in the framework or language. This adds that.

It is only a concept and a draft. Right now it works kind of correctly. When testing with ASP.Net framework (building APIs), I can jump into generated definition of built-in methods, such as .MapHub<T>(string route):

When CTRL + click on .MapHub, it generates a new temporary file and opens it in the editor. Unfortunately, the highlighter breaks right now, and it does not seem to work for built-in classes, such as Exceptions, or Task, etc. The result looks like this.

Also, I apologise for the foreign language; the compiler seems to be generating parts of the comments in the system language, I guess?

Issues Todo-list:

• Breaking syntax highlighter
• Move the "name of the folder" for temporary files and possibly its path to config/env
• We are currently persisting the generated file on the drive, that's because I couldn't find a way to pass into the Editor just a buffer -- although this itself is not bad, it can work as a cache for running session -- that's not yet implemented
• We must remove temp files on startup of the application, otherwise we will be filling the drive
• Missing ReadOnly flag for SharpIdeFile, so the generated files cannot be modified (not really an issue, I guess, more like nice to have)

I agree to the terms of contributing as stated here

[MattParkerDev]

Thanks for looking into this! Do you know if IMetadataAsSourceService handles decompiling e.g. nuget packages, or only system/runtime/sdk dlls?