Add builtins highlighting

queries/highlights.scm

@@ -49,6 +49,14 @@
     field: (identifier) @variable.member))
 ; }}}
 
+; Built-ins {{{
+[
+ (unset)
+ "default"
+] @variable.builtin
+(selection_type) @function.builtin
+; }}}
+
 ; Expressions {{{
 (map_expression
   (property

test/highlight/builtins.bp

@@ -0,0 +1,8 @@
+foo = select(soong_config_variable("my_namespace", "my_var"), {
+    //       ^ function.builtin
+    "foo": unset,
+    //     ^ variable.builtin
+    default: select(variant("VARIANT"), {}),
+    // <- variable.builtin
+    //              ^ function.builtin
+})