More support for LOX, API improvements after internal presentation, fixed bugs

[JohannesMeierSE]

I added/mixed a lot of improvements in this PR:

• improved technical infrastructure for LOX: among others, LOX can be executed as VS Code extension now
• started type checking for LOX:
  • primitives, operators, functions, classes
  • validations
  • added test cases
  • is still incomplete and WIP
• improved the Typir API according to the feedback after an internal presentation
• implemented new kind: TopKind
• started getters to reuse/find existing function types and class types, in particular, the type inference
• lots of fixed bugs and other improvements for the existing logic