Fix builtin function name highlighting

src/grammar.json

@@ -1,5 +1,6 @@
 {
   "name": "zanscript",
+  "word": "identifier",
   "rules": {
     "translation_unit": {
       "type": "REPEAT",
@@ -366,8 +367,12 @@
       "type": "SEQ",
       "members": [
         {
-          "type": "SYMBOL",
-          "name": "identifier"
+          "type": "FIELD",
+          "name": "name",
+          "content": {
+            "type": "SYMBOL",
+            "name": "identifier"
+          }
         },
         {
           "type": "STRING",

src/node-types.json

@@ -149,10 +149,21 @@
   {
     "type": "function",
     "named": true,
-    "fields": {},
+    "fields": {
+      "name": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "identifier",
+            "named": true
+          }
+        ]
+      }
+    },
     "children": {
       "multiple": true,
-      "required": true,
+      "required": false,
       "types": [
         {
           "type": "identifier",