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
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:4b3c4620166071561ec44961fb08a56676b4fd6c)
Merged-In: I3be94534dcda365da473f82347ae2e3f57bb1b42
Change-Id: I3be94534dcda365da473f82347ae2e3f57bb1b42