Add eslint-plugin-prettier and format all *_html.js

The only manual change needed to fix a test due to textContent match

Change-Id: Ic9e561f7d482e7a680b3c4bfe58decdbd5d4ec10
diff --git a/polygerrit-ui/app/elements/shared/gr-label/gr-label_html.js b/polygerrit-ui/app/elements/shared/gr-label/gr-label_html.js
index 1644c07..c4310fc 100644
--- a/polygerrit-ui/app/elements/shared/gr-label/gr-label_html.js
+++ b/polygerrit-ui/app/elements/shared/gr-label/gr-label_html.js
@@ -16,6 +16,4 @@
  */
 import {html} from '@polymer/polymer/lib/utils/html-tag.js';
 
-export const htmlTemplate = html`
-    <slot></slot>
-`;
+export const htmlTemplate = html` <slot></slot> `;