Make User::getEditCount() always return an integer

The docs comment says it returns an int but it often returned a string.
This led to casting this value into an integer in other parts of the
codebase and in extensions (grep MobileFrontend or Echo for EditCount).

Bug: 51633
Change-Id: I6fe5b26c24e674e8148c1fd278774b3fabe844c5
Merge "Make User::getEditCount() always return an integer"