This will allow extensions to inject into the query to implement
"xxshow" parameters, and to add additional properties to the output
data for "xxprop" parameters.
Also, call these new hooks from ApiQueryRevisions, ApiQueryAllRevisions,
ApiQueryUserContributions, and ApiQueryRecentChanges since I701e8e19 is
going to be wanting them.
Bug: T143614
Bug: T143616
Change-Id: Id6b42c7f2eb53a6f659d0d61383287f41d96ca00