Split intermediate representations into for each normal form

[KeenS]

currently we have only AST, HIR, MIR, LIR. However, AST have non typed phase and typed phase, and HIR has renamed (alpha converted) phase, flat_expr (K Normal) phase, flat_let (A Normal) phase.
Each phases should have its own representations

[KeenS]

raw AST
desugared AST (a.k.a Core Language)
alpha converted Core
typed Core
HIR
K Normal
A Nomal
MIR
LIR
WASM

TBD:

• How to treat Module language
• Should Core and HIR be the same?