[PATCH] Remove HIR MacroItem and other hir macro forward declarations

Almost all HIR Macro related trees were already removed by https://github.com/Rust-GCC/gccrs/pull/492 But there was still one MacroItem class left in rust-hir.h and several (unused) forward declarations in various other hir .h files. Remove them all. Resolves: https://github.com/Rust-GCC/gccrs/is

[PATCH] Handle doc comment strings in lexer and parser

Remove (unused) comment related tokens and replace them with INNER_DOC_COMMENT and OUTER_DOC_COMMENT tokens, which keep the comment text as a string. These can be constructed with the new make_inner_doc_comment and make_outer_doc_comment methods. Make sure to not confuse doc strings with normal co