Refine highlights.scm:

- Match repeat, conditional, etc. to their corresponding commands
- Clean up `@parameter` match
- Add `$ENV` and `$CACHE` to queries

queries/cmake/highlights.scm

@@ -1,19 +1,18 @@
-(bracket_content) @parameter
+[
-(quoted_element) @parameter
+ (bracket_content)
-(unquoted_argument) @parameter
+ (quoted_element)
+ (unquoted_argument)
+] @parameter
 
 (variable) @variable
 
+[
+ "$ENV"
+ "$CACHE"
+] @variable.builtin
+
 [
  (normal_command)
-  (if_command)
-  (elseif_command)
-  (else_command)
-  (endif_command)
-  (foreach_command)
-  (endforeach_command)
-  (while_command)
-  (endwhile_command)
  (function_command)
  (endfunction_command)
  (macro_command)
@@ -21,6 +20,20 @@
  (message_command)
 ] @function
 
+[
+ (if_command)
+ (elseif_command)
+ (else_command)
+ (endif_command)
+] @conditional
+
+[
+ (foreach_command)
+ (endforeach_command)
+ (while_command)
+ (endwhile_command)
+] @repeat
+
 [
  "1"
  "ON"
@@ -85,3 +98,4 @@
  "CHECK_PASS"
  "CHECK_FAIL"
 ] @keyword
+