Fix typos (#14124)

fixtures/attribute-behavior/src/App.js

@@ -860,7 +860,7 @@ class App extends React.Component {
         });
         break;
       default:
-        throw new Error('Switch statement should be exhuastive');
+        throw new Error('Switch statement should be exhaustive');
     }
 
     // Sort
@@ -887,7 +887,7 @@ class App extends React.Component {
         });
       }
       default:
-        throw new Error('Switch statement should be exhuastive');
+        throw new Error('Switch statement should be exhaustive');
     }
   }
 

packages/react-dom/src/server/escapeTextForBrowser.js

@@ -56,7 +56,7 @@ function escapeHtml(string) {
 
   let escape;
   let html = '';
-  let index = 0;
+  let index;
   let lastIndex = 0;
 
   for (index = match.index; index < str.length; index++) {

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -811,7 +811,7 @@ function mountLazyComponent(
       break;
     }
     default: {
-      // This message intentionally doesn't metion ForwardRef or MemoComponent
+      // This message intentionally doesn't mention ForwardRef or MemoComponent
       // because the fact that it's a separate type of work is an
       // implementation detail.
       invariant(