InputMethodManager: invoke ResultReceiver when returning true

After the introduction of the ZeroJankProxy [1], we unconditionally
return true from showSoftInput and hideSoftInput, indicating that we
accepted the request.

If the request then later fails, we need to report that to the result
receiver, since some apps and tests currently assume that the result
receiver will be invoked when they receive a true from the corresponding
call.

[1]: I37fd585eeccab7c3b18fb509b3607c56d800c306

Bug: 327751155
Bug: 293640003
Test: blaze test third_party/java_src/android_app/bugle/tests/instrumentation/javatests/com/google/android/apps/messaging/arigato/ui/conversation/rcs:RcsSendMultipleTest_generic_phone_master_x86_64_fullboot_en-US

Change-Id: Ie2f262128eb32db5a7922373fdfaebd2945ea36a