[PROJECT] Switching to a Salsa based backend like Rust-Analyzer

[Sarrus1]

As part of my end-of-study project, I am working on adding "real-time" lints (outside of spcomp) to sourcepawn-vscode.

The development is happening on the #feat/salsa branch, and as a result, main is frozen until this gets merged.

Using Salsa for lints will (should) yield much better performances out of the LSP. It will only compute what it needs to resolve requests, as opposed to what is currently done: parse all files and maintain a list of references for every declarations.

I will try to have a working beta as soon as possible. The goal is to have everything ready by the end of March.

List of TODOs before I can merge (will change):

• Support for multiple files
• GoToDefinition
• GoToReferences
• Completions
• Hover
• Prime caches with progress report
• Preprocessor
• Define/Macro support
• Function support
• Old function support
• Native/forward support
• Global variable support
• Local variable support
• Old variable support
• Old type support
• Array support
• Default parameters support
• Preprocessing offsetting
• Enum struct support
• Methodmap support
• Methodmap inherits support
• Enum support
• Typedef support
• Typeset support
• Functag support
• Funcenum support
• Aliases support
• Struct support
• Deprecated support
• Multiple definitions support
• Documentation parsing
• Flycheck with spcomp