Do not share key mappings with JNI object

The key mapping information between the native key mappings and
the KeyCharacterMap object available in Java is currently shared,
which means that a read can be attempted while it's being modified.

Because the code changed between R and S, this CL fixes it just
for R; the patch for versions S+ is ag/23785419

Bug: 274058082
Test: Presubmit
Change-Id: I3be94534dcda365da473f82347ae2e3f57bb1b42
Merged-In: I745008a0a8ea30830660c45dcebee917b3913d13