Change default of $wgResourceLoaderMaxQueryLength to 2000

Change default of $wgResourceLoaderMaxQueryLength to 2000

The lowest commonly supported length is a bit over 2000.  That is the limit of
Internet Explorer.  For discussion of the IE limit see
http://blogs.msdn.com/b/ieinternals/archive/2014/08/13/url-length-limits-in-internet-explorer.aspx .
Some servers only support 4k.

Having it unlimited does not work when running qunit jenkins test jobs of the
Wikibase extension or when running its qunit tests in vagrant, because it hits
the nginx limit.

This also adds a mw.track call for when the request split happens.

Bug: T90453
Change-Id: Ic416def846f361425c46f7bd1022ed85fa8ac85e