Dump IMMS#mConcurrentMultiUserModeEnabled

This field indicates if IMMS is configured for concurrent multi-user operation.
The code change is a refactoring and should not cause visible issues.

Bug: 351912418
Test: m
Test: adb shell dumpsys input_method | grep mConcurrentMultiUserModeEnabled
Test: adb shell dumpsys input_method --proto > input_method.proto && gqui from rawproto:input_method.proto --outfile=input_method.text
Flag: EXEMPT refactor
Change-Id: I124711ba1632ec85b1c56872b8ace6c5e308f12e