fix(mbe): desugar doc correctly for mbe

Fixes #16110.

The way rust desugars doc comments when expanding macros
is rendering it as raw strings delimited with hashes.
Rust-analyzer wasn't aware of this, so the desugared doc
comments wouldn't match correctly when on the LHS of macro
declarations.

This PR fixes this by porting the code used by rustc: https://github.com/rust-lang/rust/blob/4cfdbd328b7171b2328d11b950b1af0978d6b1ef/compiler/rustc_ast/src/tokenstream.rs#L6837

Author: saiintbrisson

Diff for: crates/mbe/src/syntax_bridge.rs

@@ -406,9 +406,20 @@ fn doc_comment_text(comment: &ast::Comment) -> SmolStr {
         text = &text[0..text.len() - 2];
     }
 
-    // Quote the string
+    let mut num_of_hashes = 0;
+    let mut count = 0;
+    for ch in text.chars() {
+        count = match ch {
+            '"' => 1,
+            '#' if count > 0 => count + 1,
+            _ => 0,
+        };
+        num_of_hashes = num_of_hashes.max(count);
+    }
+
+    // Quote raw string with delimiters
     // Note that `tt::Literal` expect an escaped string
-    let text = format!("\"{}\"", text.escape_debug());
+    let text = format!("r{delim}\"{text}\"{delim}", delim = "#".repeat(num_of_hashes));
     text.into()
 }