feat(grammar): support cst attribute

examples/cst.test

@@ -0,0 +1,9 @@
+====================
+Test with cst marker
+:cst
+====================
+1
+---
+0:0 - 1:0   source_file
+0:0 - 0:1   expression
+0:0 - 0:1     number_literal `1`

grammar.js

@@ -41,11 +41,12 @@ module.exports = grammar({
     ),
 
     attribute: $ => choice(
-      ":skip",
+      field("cst", ":cst"),
       ":error",
       ":fail-fast",
       $._language,
       $._platform,
+      ":skip",
     ),
 
     _language: $ => seq(

queries/test/highlights.scm

@@ -1,11 +1,12 @@
 (name) @markup.heading
 
 [
-  ":skip"
+  ":cst"
   ":error"
   ":fail-fast"
   ":language"
   ":platform"
+  ":skip"
 ] @attribute
 
 (attribute

queries/test/injections.scm

@@ -11,9 +11,30 @@
   (input) @injection.content)
 
 ((test
+  [
+    (header
+      (separator)
+      .
+      (name)
+      .
+      (separator))
+    (header
+      (attributes
+        .
+        (attribute
+          !cst)+ .))
+  ]
   (output) @injection.content)
   (#set! injection.language "query"))
 
+((test
+  (header
+    (attributes
+      (attribute
+        cst: _)))
+  (output) @injection.content)
+  (#set! injection.language "cst"))
+
 ; NOTE: custom dynamic injection
 ((test
   (header