Improve Regex syntax highlighting (#25332)

Release Notes:

  - Improved Regex syntax highlighting

| Zed 0.174.6 | With this PR |
| --- | --- |
|
![Image](https://github.com/user-attachments/assets/2a0bb1d9-cbba-490c-b2be-08c94bc79517)
|
![Image](https://github.com/user-attachments/assets/b19f3871-ee83-4165-a026-207bdbbcad44)
|

- `(?P=`, `<`: `punctuation.bracket`
- `group_name`: `property` -> `label`
- `^`, `$`: `string.escape` -> `operator`
- `\b`, `\B`, `\k`: `string.escape` -> `keyword.operator`
- added `regex` scope to target regex tokens specifically

```js
regex = /^(?<group>[!\.\?])\b[a-z]+word\k<group>$/g
```

---------

Co-authored-by: João Marcos <marcospb19@hotmail.com>

crates/languages/src/regex/highlights.scm

@@ -4,24 +4,22 @@
   "(?"
   "(?:"
   "(?<"
+  "(?P="
+  "<"
   ">"
   "["
   "]"
   "{"
   "}"
-] @string
+] @punctuation.bracket.regex
 
-(group_name) @property
+(group_name) @label.regex
 
 [
   (identity_escape)
   (control_letter_escape)
   (character_class_escape)
   (control_escape)
-  (start_assertion)
-  (end_assertion)
-  (boundary_assertion)
-  (non_boundary_assertion)
 ] @string.escape
 
 [
@@ -31,17 +29,25 @@
   "|"
   "="
   "!"
+  (start_assertion)
+  (end_assertion)
   (any_character)
-] @operator
+] @operator.regex
+
+[
+  (boundary_assertion)
+  (non_boundary_assertion)
+  (backreference_escape)
+] @keyword.operator.regex
 
 (count_quantifier
   [
     (decimal_digits) @number
-    "," @punctuation.delimiter
+    "," @punctuation.delimiter.regex
   ])
 
 (character_class
   [
-    "^" @operator
+    "^" @operator.regex
-    (class_range "-" @operator)
+    (class_range "-" @operator.regex)
   ])