Fix pattern order in C++ highlight query

Later patterns take precedence in Zed, so function names were previously
being highlighted as variables due to the plain `identifier` pattern.

crates/zed/src/languages/cpp/highlights.scm

@@ -1,3 +1,5 @@
+(identifier) @variable
+
 (call_expression
   function: (qualified_identifier
     name: (identifier) @function))
@@ -34,8 +36,6 @@
 (auto) @type
 (type_identifier) @type
 
-(identifier) @variable
-
 ((identifier) @constant
  (#match? @constant "^[A-Z][A-Z\\d_]*$"))