PrefixSearch (ApiOpenSearch) now supports searching in multiple namespaces

I thought there was just an issue with capitalization, but in fact the code
explicitly only searched one namespace anyway. Fixed that while taking
capitalization differences in namespaces into account.

Bug: 65752
Bug: 30323
Change-Id: I3487bb69eae1867832e0ec9ece497538eca32a2a
Merge "PrefixSearch (ApiOpenSearch) now supports searching in multiple namespaces"