Don't match metavariables in macro invocations

Metavariables can only occur in macro transcribers, so matching them in 
invocations makes little sense. Instead, match $ and an identifier 
separately.

Author: ninevra

grammar.js

@@ -191,7 +191,12 @@ module.exports = grammar({
     ),
 
     _non_special_token: $ => choice(
-      $._literal, $.identifier, $.metavariable, $.mutable_specifier, $.self, $.super, $.crate,
+      $._never_special_token,
+      $.metavariable
+    ),
+
+    _never_special_token: $ => choice(
+      $._literal, $.identifier, $.mutable_specifier, $.self, $.super, $.crate,
       alias(choice(...primitive_types), $.primitive_type),
       /[/_\-=->,;:::!=?.@*&#%^+<>|~]+/,
       '\'',
@@ -906,7 +911,7 @@ module.exports = grammar({
     ),
 
     _non_delim_token: $ => choice(
-      $._non_special_token,
+      $._never_special_token,
       '$'
     ),
 

src/grammar.json

@@ -658,15 +658,24 @@
       "members": [
         {
           "type": "SYMBOL",
-          "name": "_literal"
+          "name": "_never_special_token"
         },
         {
           "type": "SYMBOL",
-          "name": "identifier"
+          "name": "metavariable"
+        }
+      ]
+    },
+    "_never_special_token": {
+      "type": "CHOICE",
+      "members": [
+        {
+          "type": "SYMBOL",
+          "name": "_literal"
         },
         {
           "type": "SYMBOL",
-          "name": "metavariable"
+          "name": "identifier"
         },
         {
           "type": "SYMBOL",
@@ -5026,7 +5035,7 @@
       "members": [
         {
           "type": "SYMBOL",
-          "name": "_non_special_token"
+          "name": "_never_special_token"
         },
         {
           "type": "STRING",