Language button icon/button should be consistent with other buttons

This converts the language button into a mw-ui-button which is the
class we're currently using in both Vector and Minerva. In future
this can become a WVUI button using the same roadmap as Vector
and Minerva.

This fixes the issue with the icon resize, as well as the issue
with the button lacking appropriate hover/focus states.

Bug: T289630
Change-Id: I8242986e8762a8f663f8cab07c54481e14223320

resources/css/ext.uls.pt.less

@@ -19,23 +19,29 @@
  * A hack to load the icon before the rest of the module is lazy-loaded.
  * Copied from jquery.uls.css with the path changed.
  */
-.uls-trigger {
+.uls-trigger a:before {
 	background: no-repeat url( ../../lib/jquery.uls/images/language.svg ) left center;
-	// Let the SVG image fit without cropping or stretch
-	background-size: contain;
-	padding-left: 24px;
 }
 
+.vector-user-links {
+	.uls-trigger {
+		// Disable additional icon on load.
+		background-image: none;
+		// Can be removed when no longer need to override rule in jquery.uls.css
+		padding-left: 12px;
+	}
+}
+
+// Vector modern = ca-uls
+// Other skins = pt-uls
 #pt-uls {
-	padding-top: 0 !important; // stylelint-disable-line declaration-no-important
+	.mw-ui-button {
+		display: inline;
+		padding: 0;
+		border: 0;
+	}
 
 	.uls-trigger {
-		background-image: none;
-		// Same values as Vector's `#p-personal li`.
-		display: inline-block;
-		padding-top: 0.5em !important; // stylelint-disable-line declaration-no-important
-		padding-left: 0;
-
 		// Putting the icon in before in order to apply `opacity`.
 		&:before {
 			content: '';
@@ -53,6 +59,12 @@
 	}
 }
 
+.skin-vector {
+	#ca-uls span {
+		font-size: 0.875em;
+	}
+}
+
 /* Opera for some inexplicable reason confuses right and left padding with */
 /* RTL text direction here (bug T47142). x:-o-prefocus won't match anything, */
 /* but will make other browsers ignore this rule. */