Rename hiddenAPIFlagFileInfo to HiddenAPIInfo

This reflects that it has expanded from its initial purpose to include
more than just flag files. It is exported for use in tests in other
packages.

Bug: 179354495
Test: m nothing
Merged-In: I9f780b20e18ce3a774e4aa04a276463070a64c34
Change-Id: I9f780b20e18ce3a774e4aa04a276463070a64c34
(cherry picked from commit af99afa9)