tools: auto fix custom eslint rule for no-unescaped-regexp-dot

1. Added fixer method for resolving lint error.
2. Added additional valid tests + Output for current and new invalid tests.

Refs: nodejs#16636

Author: shobhitchittora

test/parallel/test-eslint-no-unescaped-regexp-dot.js

@@ -13,16 +13,26 @@ new RuleTester().run('no-unescaped-regexp-dot', rule, {
     '/.*/',
     '/.?/',
     '/.{5}/',
-    String.raw`/\\\./`
+    String.raw`/\\\./`,
+    RegExp(/^\.$/),
+    RegExp(/^.+$/),
+    RegExp(/^\\\.$/),
   ],
   invalid: [
     {
       code: '/./',
-      errors: [{ message: 'Unescaped dot character in regular expression' }]
+      errors: [{ message: 'Unescaped dot character in regular expression' }],
+      output: '/\\./'
     },
     {
       code: String.raw`/\\./`,
-      errors: [{ message: 'Unescaped dot character in regular expression' }]
+      errors: [{ message: 'Unescaped dot character in regular expression' }],
+      output: String.raw`/\./`,
+    },
+    {
+      code: 'RegExp(/^\\.$/)',
+      errors: [{ message: 'Unescaped dot character in regular expression' }],
+      output: RegExp(/^\.$/),
     }
   ]
 });

tools/eslint-rules/no-unescaped-regexp-dot.js

@@ -16,10 +16,29 @@ module.exports = function(context) {
 
   function report(node, startOffset) {
     const indexOfDot = sourceCode.getIndexFromLoc(node.loc.start) + startOffset;
+    const expression = sourceCode.getText(node);
+    const dotOffset = expression.indexOf('.');
+    var correctedExpression = '';
+
+    if (expression.charAt(dotOffset - 1) === '\\') {
+      correctedExpression = expression.slice(0, dotOffset - 1) +
+                            expression.slice(dotOffset);
+    } else {
+      correctedExpression = expression.slice(0, dotOffset) +
+                            '\\' +
+                            expression.slice(dotOffset);
+    }
+
     context.report({
       node,
       loc: sourceCode.getLocFromIndex(indexOfDot),
-      message: 'Unescaped dot character in regular expression'
+      message: 'Unescaped dot character in regular expression',
+      fix: (fixer) => {
+        return fixer.replaceText(
+          node,
+          correctedExpression
+        );
+      }
     });
   }