mediawiki.inspect: Fix exception when calling mw.inspect() a second time

mediawiki.inspect: Fix exception when calling mw.inspect() a second time

In mediawiki.js, the mw.inspect() method is defined to lazy-load the
'mediawiki.inspect' module, and then call mw.inspect.runReports().

The problem is that, mediawiki.inspect.js, re-creates mw.inspect as a plain
object, which blows away the mw.inspect() function that was there.

Calling it a second time threw "TypeError: inspect is not a function".

Fix this by making mediawiki.inspect.js extend the function object,
instead of re-defining it.

Bug: T197810
Change-Id: I61aa965f3e1fd0a1c9f9d98310632b4a8d5e1683