languages: Fix C/C++ preprocessor directive highlight regression (#49031)

## Summary

- PR #48109 changed the capture name for C/C++ preprocessor directives
from `@keyword.directive` to `@preproc`. While semantically correct, the
builtin themes had `preproc` defined with colors nearly
indistinguishable from plain text (e.g. One Dark `#dce0e5ff`, Ayu Dark
`#bfbdb6ff`), making `#include`, `#define`, etc. appear unhighlighted.
- This PR updates the `preproc` color in all builtin themes (and the
fallback theme) to match their respective `keyword` color, restoring
visible highlighting for preprocessor directives.

Fixes #49024

## Side effects

- Go uses `@preproc` for `//go:` and `// +build` compiler directives.
These will also change from the previous muted gray to the keyword
color. This is arguably an improvement — compiler directives are special
constructs that benefit from visible highlighting, consistent with how
other editors (CLion, VS Code) handle them.

## Test plan

- [x] `cargo test -p language highlight_map` passes
- [x] Open a C/C++ file and verify `#include`, `#define`, `#ifdef`, etc.
are highlighted with the keyword color
- [x] Verify across multiple builtin themes (One Dark, Ayu Dark, Gruvbox
Dark, etc.)
- [x] Open a Go file and verify `//go:` directives are highlighted
reasonably

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Release Notes:

- Fixed C/C++ preprocessor directives (`#include`, `#define`, etc.)
appearing unhighlighted in builtin themes.

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: MrSubidubi <finn@zed.dev>

assets/themes/ayu/ayu.json

@@ -283,7 +283,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#bfbdb6ff",
+            "color": "#ff8f3fff",
             "font_style": null,
             "font_weight": null
           },
@@ -685,7 +685,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#5c6166ff",
+            "color": "#fa8d3eff",
             "font_style": null,
             "font_weight": null
           },
@@ -1087,7 +1087,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#cccac2ff",
+            "color": "#ffad65ff",
             "font_style": null,
             "font_weight": null
           },

assets/themes/gruvbox/gruvbox.json

@@ -293,7 +293,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#fbf1c7ff",
+            "color": "#fb4833ff",
             "font_style": null,
             "font_weight": null
           },
@@ -710,7 +710,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#fbf1c7ff",
+            "color": "#fb4833ff",
             "font_style": null,
             "font_weight": null
           },
@@ -1127,7 +1127,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#fbf1c7ff",
+            "color": "#fb4833ff",
             "font_style": null,
             "font_weight": null
           },
@@ -1544,7 +1544,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#282828ff",
+            "color": "#9d0006ff",
             "font_style": null,
             "font_weight": null
           },
@@ -1961,7 +1961,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#282828ff",
+            "color": "#9d0006ff",
             "font_style": null,
             "font_weight": null
           },
@@ -2378,7 +2378,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#282828ff",
+            "color": "#9d0006ff",
             "font_style": null,
             "font_weight": null
           },

assets/themes/one/one.json

@@ -290,7 +290,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#dce0e5ff",
+            "color": "#b477cfff",
             "font_style": null,
             "font_weight": null
           },
@@ -702,7 +702,7 @@
             "font_weight": null
           },
           "preproc": {
-            "color": "#242529ff",
+            "color": "#a449abff",
             "font_style": null,
             "font_weight": null
           },

crates/grammars/src/c/highlights.scm

@@ -38,7 +38,7 @@
   "#ifndef"
   "#include"
   (preproc_directive)
-] @preproc
+] @keyword.preproc @preproc
 
 [
   "="

crates/grammars/src/cpp/highlights.scm

@@ -196,7 +196,7 @@ type: (primitive_type) @type.builtin
   "#ifndef"
   "#include"
   (preproc_directive)
-] @preproc
+] @keyword.preproc @preproc
 
 (comment) @comment
 

crates/theme/src/fallback_themes.rs

@@ -357,7 +357,7 @@ pub(crate) fn zed_default_dark() -> Theme {
                 ("number".into(), orange.into()),
                 ("operator".into(), HighlightStyle::default()),
                 ("predictive".into(), HighlightStyle::default()),
-                ("preproc".into(), HighlightStyle::default()),
+                ("preproc".into(), purple.into()),
                 ("primary".into(), HighlightStyle::default()),
                 ("property".into(), red.into()),
                 ("punctuation".into(), HighlightStyle::default()),