Use strict equality as a guard before assigning input.value

This commit adds back the guard around assigning the value property to
an input, however it does it using a strict equals. This prevents
validated inputs, like emails and urls from losing the cursor
position.

It also adds associated test fixtures.

fixtures/dom/src/components/fixtures/text-inputs/index.js

@@ -43,6 +43,34 @@ class TextInputFixtures extends React.Component {
           </p>
         </TestCase>
 
+        <TestCase title="Cursor when editing email inputs">
+          <TestCase.Steps>
+            <li>Type "user@example.com"</li>
+            <li>Select "@"</li>
+            <li>Type ".", to replace "@" with a period</li>
+          </TestCase.Steps>
+
+          <TestCase.ExpectedResult>
+            The text field's cursor should not jump to the end.
+          </TestCase.ExpectedResult>
+
+          <InputTestCase type="email" defaultValue="" />
+        </TestCase>
+
+        <TestCase title="Cursor when editing url inputs">
+          <TestCase.Steps>
+            <li>Type "http://www.example.com"</li>
+            <li>Select "www."</li>
+            <li>Press backspace/delete</li>
+          </TestCase.Steps>
+
+          <TestCase.ExpectedResult>
+            The text field's cursor should not jump to the end.
+          </TestCase.ExpectedResult>
+
+          <InputTestCase type="url" defaultValue="" />
+        </TestCase>
+
         <TestCase title="All inputs" description="General test of all inputs">
           <InputTestCase type="text" defaultValue="Text" />
           <InputTestCase type="email" defaultValue="user@example.com"/>

src/renderers/dom/fiber/wrappers/ReactDOMFiberInput.js

@@ -209,8 +209,7 @@ var ReactDOMInput = {
           // browsers typically do this as necessary, jsdom doesn't.
           node.value = '' + value;
         }
-        // eslint-disable-next-line
-      } else {
+      } else if (node.value !== value) {
         // Cast `value` to a string to ensure the value is set correctly. While
         // browsers typically do this as necessary, jsdom doesn't.
         node.value = '' + value;

src/renderers/dom/stack/client/wrappers/ReactDOMInput.js

@@ -201,8 +201,7 @@ var ReactDOMInput = {
           // browsers typically do this as necessary, jsdom doesn't.
           node.value = '' + value;
         }
-        // eslint-disable-next-line
-      } else {
+      } else if (node.value !== value) {
         // Cast `value` to a string to ensure the value is set correctly. While
         // browsers typically do this as necessary, jsdom doesn't.
         node.value = '' + value;