Rename mw.util.wikiGetlink to getUrl

Old name still works, but is deprecated.

The new one has the nice property of being the same as a function
defined on mw.Title which does the same thing.

Replaced all occurences throughout the codebase.

Bug: 55764
Change-Id: I8704a6620ece44d374e199c05464b8a553e12e74