Change ULS content language selector positioning

New Vector introduced a new content language selector trigger. This
code was hardcoding a behavior that works for compact language links
but is not so appropriate for other uses in the skin, which are out
of our control.

This patch aims to be a minimal change to allow other kinds of
behavior without changing the amount of tech debt. This changes
the default ULS dialog behavior to match the requirements shown
in the task. Compact language links specific behavior is retained but
only enabled for the compact language links trigger. The behavior
is chosen depending on the value of isUsingStandaloneLanguageButton().

For future changes, I propose that mw-interlanguage-selector class will
not have any styles attached to it. Whoever creates the trigger would
be in charge of styling it. Ideally that code would also define the
positioning and other behavior, but it is less clear how that can be
abstracted in a nice and decoupled way.

Bug: T276248
Change-Id: I52da6c2f5a1f25d64f322a3c8f6105da3b244b66

resources/css/ext.uls.compactlinks.less

@@ -27,6 +27,10 @@
 	background-color: #c8ccd1;
 }
 
+/*
+ * Add caret to the ULS dialog when using the cog in the sidebar.
+ * This works together with selector-left and selector-right classes.
+ */
 .interlanguage-uls-menu {
 	.caret();
 }