Standard C# libs(System, etc.) giving errors in VSCode until the project solution is built

[atirut-w]

Godot version

v3.4.4.stable.mono.official [419e713]

System information

Fedora 35

Issue description

When you initially create a C# script and open it in VSCode(with C#, Mono Debug and C# Godot Tools extensions installed), there are errors that do not make sense such as using System; not working.

They all go away after running the project(and thus building the project solution) and optionally restarting OmniSharp

Steps to reproduce

1. Create a project
2. Create a new C# script
3. A bunch of errors about System not being there
4. Run the project
5. Optionally restart OmniSharp
6. Errors are gone

Minimal reproduction project

No response

[Flavelius]

Somewhat related to that, even when downloading c# addons from the asset library there are similar errors.
I think there are certain valid points in the pipeline where an automatic build/compile, triggered by godot should alleviate many problems.

[Calinou]

Related to godotengine/godot-proposals#849.