Use UA styles rather than prose to define <input> clip

The previous prose to make `overflow` act as `visible` with regards to other CSS features but still clip didn't work well with e.g. `text-overflow: ellipsis`. CSS now has a standard way to do what `input` buttons need, i.e. clip and also not affect interaction with `vertical-align`.

Fixes whatwg#9976.

source

@@ -131501,6 +131501,11 @@ input, select, button, textarea {
   appearance: auto;
 }
 
+input:not([type=image i]) {
+  overflow: clip !important;
+  overflow-clip-margin: 0 !important;
+}
+
 input, select, textarea {
   text-align: initial;
 }
@@ -131540,11 +131545,6 @@ input:not([type=image i]), textarea { box-sizing: border-box; }</code></pre>
 
   <ul>
    <li><p>The <span>inner display type</span> is always 'flow-root'.</p></li>
-
-   <li><p>The <span>'overflow'</span> property is ignored, and always behaves as 'visible' for the
-   purpose of interaction with other CSS features (in particular, the <span>'vertical-align'</span>
-   property), but still clips any overflow at the border edge, and no scrolling mechanism is
-   displayed.</p></li>
   </ul>