Populate LookupInputWidget on mousedown too

We were relying on this already having happened
on focus, but population on focus can now be
prevented through setLookupsDisabled().

Note that:
* We don't repopulate if the menu is already open
* For a mousedown firing immediately after a focus,
  populateLookupMenu() will filter the duplicate call
* For a mousedown some amount of time after a focus
  while the same value is still in the input, the
  lookup will be in cache

Bug: 72959
Change-Id: I2b037b7183429ed4111f670b3566a6fe10c6f3ff
Merge "Populate LookupInputWidget on mousedown too"