Eliminate HIR in favor of AST-specific queries

[fabianschuiki]

HIR has been carried over from the early days of moore as a way to establish parent relationships and perform high-level analysis of AST nodes. Since AST nodes now properly carry their parent, the only remaining use case of the HIR is high-level analyses of AST nodes (like splitting pattern exprs into repeat patterns, positional patterns, etc.). These would be much better expressed as queries operating specifically on those AST nodes, and get rid of the HIR in the process.

The following HIR nodes and lowerings need to be dropped in favor of more specific queries:

• Expressions
  • Patterns
  • Calls to builtin functions (e.g. $bits(...))