Fix camel-case-related lint erros under a.i.navigationbar

This is a mechanical cleanup CL.  There should be no behavior change.

Bug: 215443343
Test: prebuilts/checkstyle/checkstyle.py -f \
  frameworks/base/core/java/android/inputmethodservice/navigationbar/ \
  | grep "camel-case"
Change-Id: I05b25b11c6b571407bc4a707161fb993960603f9