Move testapi API files for symmetry with others

The other non-updatable API files are in core/api/*. Also add
-non-updatable to the module to match the others.

Bug: 171029603
Test: m checkapi
Change-Id: I2bd1fa5bac6b35096b3059f93d68ef24b7a464e5
Merged-In: I2bd1fa5bac6b35096b3059f93d68ef24b7a464e5
(cherry picked from commit 3a1b1bd620454dd1d5b328c98634a567865cd55e)