Register meta data to allow Vector to handle display of this menu item

- Adjusts CSS to defer button/icon rendering to skins that support button
and icons e.g. Vector

Depends-On: Ib518858e06549f252d73d57fd4768f446cc561b9
Bug: T289630
Change-Id: Ie9e30af5468aea9803d77c9a36e480ba2b2e86a0

resources/css/ext.uls.pt.less

@@ -24,6 +24,13 @@
 	// Let the SVG image fit without cropping or stretch
 	background-size: contain;
 	padding-left: 24px;
+
+	// Certain skins upgrade this to mw-ui-button. Background and padding should not apply.
+	// e.g. Modern Vector
+	&.mw-ui-button {
+		background: none;
+		padding-left: 12px;
+	}
 }
 
 #pt-uls {