jquery.makeCollapsible: fix jQuery memory leak

jQuery saves event data in jQuery.cache and magically clears it when
relevant elements are removed from DOM. However, if an element is
created, has event handlers attached and is never added to the DOM,
it never gets a chance to clear the data, resulting in a memory leak.

Only build the default toggle link when needed to avoid this.

Bug: 49626
Change-Id: I0c92e5c28a66c6a6469e107593dc9b6d3baa8a10
Merge "jquery.makeCollapsible: fix jQuery memory leak"