Revert "Use custom parser for gts/gjs (ember-cli#1920)"

This reverts commit 9bd5ee4.

lib/config/recommended.js

@@ -1,4 +1,5 @@
 const rules = require('../recommended-rules');
+const util = require('ember-template-imports/src/util');
 
 module.exports = {
   root: true,
@@ -28,12 +29,11 @@ module.exports = {
      * on -- and isn't relevant to user-land code.
      */
     {
-      files: ['**/*.gts'],
-      parser: require.resolve('../parsers/gts-parser'),
-    },
-    {
-      files: ['**/*.gjs'],
-      parser: require.resolve('../parsers/gjs-parser'),
+      files: ['**/*.gjs', '**/*.gts'],
+      processor: 'ember/<template>',
+      globals: {
+        [util.TEMPLATE_TAG_PLACEHOLDER]: 'readonly',
+      },
     },
   ],
 };

lib/index.js

@@ -2,10 +2,18 @@
 
 const requireIndex = require('requireindex');
 
+const gjs = require('./preprocessors/glimmer');
+
 module.exports = {
   rules: requireIndex(`${__dirname}/rules`),
   configs: requireIndex(`${__dirname}/config`),
   utils: {
     ember: require('./utils/ember'),
   },
+  processors: {
+    // https://eslint.org/docs/developer-guide/working-with-plugins#file-extension-named-processor
+    '.gjs': gjs,
+    '.gts': gjs,
+    '<template>': gjs,
+  },
 };