[FEATURE] Semantic tokens

[SpontanCombust]

Add semantic tokens LSP feature
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_semanticTokens

Use cases:

• Proper variable coloring. Variable tokens should have different token classes assigned to them depending on whether they are locals, fields, const fields, parameters or enum members.
• Unused variables should be grayed out
• Struct constructors should be colored like types