Draft: Frontend Pruning

type:internal

This MR follows !2001 (merged) by removing passes 06-09 and the Ast_sugar stage. This is achieved by re-adding sugared constructs into Ast_core and Ast_typed

Some minor additional changes are performed in this MR (in preparation for future work) such as:

• Functorizing Let_in, Rows and Record

Changelog details:

Remove dead passes and code from the frontend