BagOStuff: Optionally log duplicate key lookups

BagOStuff: Optionally log duplicate key lookups

Add new 'reportDupes' parameter to BagOStuff. This parameter enables scheduling
of a callback after the current web request ends. This callback will emit warning
log messages for all keys that were requested more than once.

The default ObjectCache factory for MediaWiki enables this option by default.
Not by default for plain BagOStuff instances, however. E.g. `new HashBagOStuff()`.

It also set 'asyncHandler' for all classes now (not just MultiWriteBagOStuff).

Bug: T128125
Co-Authored-By: Timo Tijhof <krinklemail@gmail.com>
Change-Id: I8a2b06cf54d2acf5950eed71756ecdf50e224be1