This is needed because the $params array is then passed on to
ApiEditPage, so if the hook implementer wants to alter the data used
with the edit, it needs to be able to modify the $params.
See I494d72a42d9103c28c4d44077cfe0f1269fc7b00 for an example where
GrowthExperiments would like to modify the 'tags' parameter for an
edit.
Depends-On: Idd052281898f99e4f13f241d5633294b59b29329
Bug: T304747
Change-Id: Ia4842a1593028f5fa145de167ccf9b72efa81351
This is more a proof of concept. The PHP code in this codebase
is rather small, but not trivial, and worth being covered by
tests.
Change-Id: I20c713c3c3be5d289947a343cd4fbf5256234a4a