DEV: Correct typos and spelling mistakes (#12812)

Over the years we accrued many spelling mistakes in the code base. 

This PR attempts to fix spelling mistakes and typos in all areas of the code that are extremely safe to change 

- comments
- test descriptions
- other low risk areas

lib/javascripts/messageformat.js

@@ -10,7 +10,7 @@
 */
 (function ( root ) {
 
-  // Create the contructor function
+  // Create the constructor function
   function MessageFormat ( locale, pluralFunc ) {
     var fallbackLocale;
 
@@ -133,7 +133,7 @@
     
     var result = {
       /*
-       * Parses the input with a generated parser. If the parsing is successfull,
+       * Parses the input with a generated parser. If the parsing is successful,
        * returns a value explicitly or implicitly specified by the grammar from
        * which the parser was generated (see |PEG.buildParser|). If the parsing is
        * unsuccessful, throws |PEG.parser.SyntaxError| describing the error.

lib/javascripts/widget-hbs-compiler.js

@@ -125,7 +125,7 @@ function mustacheValue(node, state) {
       return `${useHelper(state, "iconNode")}(${valueOf(node.params[0])})`;
       break;
     default:
-      // Shortcut: If our mustach has hash arguments, we can assume it's attaching.
+      // Shortcut: If our mustache has hash arguments, we can assume it's attaching.
       // For example `{{home-logo count=123}}` can become `this.attach('home-logo, { "count": 123 });`
       let hash = node.hash;
       if (hash.pairs.length) {