Add horizontal resizability to autocomplete popup (elastic#180243)

## Summary

This PR adds horizontal resizability to the autocomplete popup. The
resized width does not persist, so it returns to the default on every
load.

Closes elastic#171268
Closes elastic#125186

### CSS resizer on Safari

The CSS resizer behaves uniquely on Safari. You can't resize an element
if another element overlaps the resizer like this.

```html
data:text/html,<div%20style="position:fixed;width:280px;height:128px;resize:both;border:solid%201px;overflow:hidden;"><div%20style="position:absolute;right:0px;bottom:0px;">FOO<div></div>
```

The workaround is to set a negative z-index to the overlapping element
like this.

```html
data:text/html,<div%20style="position:fixed;width:280px;height:128px;resize:both;border:solid%201px;overflow:hidden;"><div%20style="position:absolute;right:0px;bottom:0px;z-index:-1;">FOO<div></div>
```

## Release note

Adds horizontal resizability to the autocomplete popup on the Dev Tools
Console

---------

Co-authored-by: Michael Marcialis <[email protected]>

src/plugins/console/public/styles/_index.scss

@@ -7,3 +7,15 @@
 
 @import 'app';
 @import 'components/index';
+
+.ace_editor.ace_autocomplete {
+  resize: horizontal;
+
+  // These negative z-index's ensure to expose the resizer on Safari.
+  .ace_scroller {
+    z-index: -1;
+  }
+  .ace_scrollbar.ace_scrollbar-v {
+    z-index: -1;
+  }
+}