Merge #11444

11444: feat: Fix up syntax errors in attribute macro inputs to make completion work more often r=flodiebold a=flodiebold

This implements the "fix up syntax nodes" workaround mentioned in #11014. It isn't much more than a proof of concept; I have only implemented a few cases, but it already helps quite a bit.

Some notes:
 - I'm not super happy about how much the fixup procedure needs to interact with the syntax node -> token tree conversion code (e.g. needing to share the token map). This could maybe be simplified with some refactoring of that code.
 - It would maybe be nice to have the fixup procedure reuse or share information with the parser, though I'm not really sure how much that would actually help.

Co-authored-by: Florian Diebold <flodiebold@gmail.com>

crates/ide_completion/src/tests/attribute.rs

@@ -62,8 +62,7 @@ fn proc_macros_qualified() {
 struct Foo;
 "#,
         expect![[r#"
-            at input_replace pub macro input_replace
-            at identity      pub macro identity
+            at identity pub macro identity
         "#]],
     )
 }