Fix crash in non-indexable keys collection

Some of the AmbientDisplay preference controllers were
crashing when their isAvailable methods were being called
by their fragment's search index providers, which meant that
the entire collection of non-indexable keys failed. Thus,
all search results were showing up. In the case of a secondary
user, they were able to see developer options which crashed
settings when clicked.

There are two issues addressed in this cl.
1. Fix the crashes so the non-indexable keys collection works
2. Contain each fragment's collection, so that if a fragment does
crash, the damage is minimized.

Part 1 is checking that the config in isAvailable is not null,
and creating one if so.

Part 2 is fixed by surrounding the collection of non-indexable
keys in a try-catch, with an option in the catch to re-throw the
error if a system property is set. Thus, in a new pre-submit
instrumentation test, we can and docheck if any of the fragments crash
when collecting non-indexable keys.

Change-Id: I820bd9cb2649aa6faff7f82fcf575a62e41dc4fc
Fixes: 77486668
Test: atest NonIndexableCrashTest, robotests