Surround <input is="iron-input"> with <iron-input>

Type extension does not work anymore in Polymer 2:
https://polymer-library.polymer-project.org/2.0/docs/about_20#type-extension

Recommendation by Polyer expert was:
Most of the time, you can do
<iron-input params...>
  <input is="iron-input" thoseSameParams...>
</iron-input>

id attributes were kept at the <input> element, not moved to the
<iron-input> element. This may mean that in Polymer 2 some still tests
are still failing that look up input elements by id. Will fix this in
a follow-up change.

The goal was to create a simple non-breaking change across the entire
code base. There might still be some issues running this with Polymer 2.

This change also clean ups iron-input html imports. Some could be
removed, some had to be added.

Change-Id: I48361ff465990246622ec8ad23d80b75f40cc055

polygerrit-ui/app/elements/change/gr-confirm-cherrypick-dialog/gr-confirm-cherrypick-dialog.html

@@ -15,8 +15,9 @@ See the License for the specific language governing permissions and
 limitations under the License.
 -->
 
-<link rel="import" href="/bower_components/iron-autogrow-textarea/iron-autogrow-textarea.html">
 <link rel="import" href="/bower_components/polymer/polymer.html">
+<link rel="import" href="/bower_components/iron-autogrow-textarea/iron-autogrow-textarea.html">
+<link rel="import" href="/bower_components/iron-input/iron-input.html">
 <link rel="import" href="../../../styles/shared-styles.html">
 <link rel="import" href="../../shared/gr-autocomplete/gr-autocomplete.html">
 <link rel="import" href="../../shared/gr-dialog/gr-dialog.html">
@@ -77,12 +78,17 @@ limitations under the License.
         <label for="baseInput">
           Provide base commit sha1 for cherry-pick
         </label>
-        <input
-            is="iron-input"
-            id="baseCommitInput"
+        <iron-input
             maxlength="40"
             placeholder="(optional)"
             bind-value="{{baseCommit}}">
+          <input
+              is="iron-input"
+              id="baseCommitInput"
+              maxlength="40"
+              placeholder="(optional)"
+              bind-value="{{baseCommit}}">
+        </iron-input>
         <label for="messageInput">
           Cherry Pick Commit Message
         </label>