Add parsers object to RuleParams type, annotate every rule definition with Rule type for better type validation.

lib/md047.js

@@ -4,6 +4,8 @@
 
 const { addError, isBlankLine } = require("../helpers");
 
+// eslint-disable-next-line jsdoc/valid-types
+/** @type import("./markdownlint").Rule */
 module.exports = {
   "names": [ "MD047", "single-trailing-newline" ],
   "description": "Files should end with a single newline character",
@@ -15,8 +17,8 @@ module.exports = {
       addError(
         onError,
         lastLineNumber,
-        null,
-        null,
+        undefined,
+        undefined,
         [ lastLine.length, 1 ],
         {
           "insertText": "\n",