Improve Rust highlight queries (#16747)

Release Notes:

- Add `@variable.parameter` highlight scope

![parameters are colored
pink](https://github.com/user-attachments/assets/68920017-b191-4779-9aa6-856831938480)

- Add `@attribute` highlight scope

![attributes are colored
yellow](https://github.com/user-attachments/assets/558d6ce0-5e4c-4ecb-893c-bc8f88d63829)

- Add markdown injection inside `doc_comment`s

![markdown
highlighting](https://github.com/user-attachments/assets/93ef4cf6-5ac1-46c6-80d0-82ca7bee0447)

crates/languages/src/rust/highlights.scm

@@ -184,3 +184,8 @@
 ] @operator
 
 (lifetime) @lifetime
+
+(parameter (identifier) @variable.parameter)
+
+(attribute_item) @attribute
+(inner_attribute_item) @attribute

crates/languages/src/rust/injections.scm

@@ -5,3 +5,11 @@
 (macro_rule
   (token_tree) @content
   (#set! "language" "rust"))
+
+(block_comment
+  (doc_comment) @content
+  (#set! "language" "markdown"))
+
+(line_comment
+  (doc_comment) @content
+  (#set! "language" "markdown"))