Merge #2628

Merge #2628

2628: Add macro 2.0 support in parser r=matklad a=edwin0cheng

This PR added a new syntax kind : `MACRO_DEF` and a keyword `MACRO_KW`

there are two syntax for declarative macro 2.0 :
1. Normal : `macro m { ($i:ident) => {} }` , which handle similar to legacy one.
2. Call like: `macro m($i:ident) {}`, it produces a single token tree which have two child token trees : `($i:ident)` and `{}`

Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>