Chore: enable a modified version of multiline-comment-style on codebase (#9452)

This makes the following changes:

* Creates a project-specific `multiline-comment-style` rule,
  which is the same as the built-in `multiline-comment-style` rule
  except that it ignores the banner comments that we use at the top of
  files.
* Enables the `multiline-comment-style` rule on the ESLint
codebase

Author: not-an-aardvark

.eslintrc.js

@@ -24,6 +24,7 @@ module.exports = {
         "eslint-plugin/prefer-placeholders": "error",
         "eslint-plugin/report-message-format": ["error", "[^a-z].*\\.$"],
         "eslint-plugin/test-case-property-ordering": "error",
-        "eslint-plugin/test-case-shorthand-strings": "error"
+        "eslint-plugin/test-case-shorthand-strings": "error",
+        "rulesdir/multiline-comment-style": "error"
     }
 };

Makefile.js

@@ -843,9 +843,11 @@ target.checkRuleFiles = function() {
             const docText = cat(docFilename);
             const idOldAtEndOfTitleRegExp = new RegExp(`^# (.*?) \\(${id}\\)`); // original format
             const idNewAtBeginningOfTitleRegExp = new RegExp(`^# ${id}: `); // new format is same as rules index
-            // 1. Added support for new format.
-            // 2. Will remove support for old format after all docs files have new format.
-            // 3. Will remove this check when the main heading is automatically generated from rule metadata.
+            /*
+             * 1. Added support for new format.
+             * 2. Will remove support for old format after all docs files have new format.
+             * 3. Will remove this check when the main heading is automatically generated from rule metadata.
+             */
 
             return idNewAtBeginningOfTitleRegExp.test(docText) || idOldAtEndOfTitleRegExp.test(docText);
         }