Updates IR_VERSION to 3. In an effort to support more features of the
Nix language, implements 5 new node type constants:
- `LAMBDA_PATTERN` = `0x70` - Lambda with pattern matching
- `INHERIT` = `0x71` - Simple inherit expressions
- `INHERIT_FROM` = `0x72` - Inherit from source expression
- `STRING_INTERPOLATION` = `0x73` - String with interpolated parts
- `BUILTIN_CALL` = `0x74` - Builtin function call
and some struct definitions before the Node class, such as `PatternField`.
Those will come in handy for suppporting the entire Nixpkgs library.
Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I1f0e81a120a0c956b8068d81c42796616a6a6964
