Support for source generators

Issue Type: Bug

.Net team introduced source generators and OmniSharp doesn’t work correctly with them.

I enabled Analyzers in VS Code and this works well. After I added a source generator to a project Intellisense doesn’t work in the source generator file and I see errors in log.

[warn]: OmniSharp.Roslyn.CSharp.Workers.Diagnostics.AnalyzerWorkQueue
        Timeout before work got ready for foreground analysis queue. This is assertion to prevent complete api hang in case of error.
[fail]: OmniSharp.MSBuild.ProjectManager
        Failure while loading the analyzer reference 'TypeCatalogGenenerator': Could not load file or assembly 'System.Runtime, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
[warn]: OmniSharp.Roslyn.CSharp.Workers.Diagnostics.AnalyzerWorkQueue
        Timeout before work got ready for foreground analysis queue. This is assertion to prevent complete api hang in case of error.
[warn]: OmniSharp.Roslyn.CSharp.Workers.Diagnostics.AnalyzerWorkQueue
        Timeout before work got ready for foreground analysis queue. This is assertion to prevent complete api hang in case of error.

It seems OmniSharp run the source generator like an analyzer although it shouldn’t have to.

Extension version: 1.23.6 VS Code version: Code 1.51.1 (e5a624b788d92b8d34d1392e4c4d9789406efe8f, 2020-11-10T23:34:32.027Z) OS version: Windows_NT x64 10.0.18363

System Info

Item	Value
CPUs	Intel® Core™ i5-2410M CPU @ 2.30GHz (4 x 2295)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on oop_rasterization: unavailable_off opengl: enabled_on protected_video_decode: unavailable_off rasterization: unavailable_off skia_renderer: disabled_off_ok video_decode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	3.91GB (0.53GB free)
Process Argv	–crash-reporter-id a4f7808b-f735-44a7-add9-c658fbcfd849
Screen Reader	no
VM	0%

[333fred]

They will be in the next release of the vscode extension, I believe.

[333fred]

https://github.com/OmniSharp/omnisharp-vscode/pull/5339 will add support for find-references when the result exists in a generated file. Features in the generated files themselves (such as find references, outline viewer, etc) need work to be enabled.