Remove the dependency on InputMethodSettings

InputMethodUtils.InputMethodSetting is a quite complicated inernal
class of InputMethodUtils and PhysicalKeyboardFragment's depending on
it just for getting/setting SHOW_IME_WITH_HARD_KEYBOARD is overkill.

With this CL, PhysicalKeyboardFragment just uses Secure Settings APIs
directly.

There should be no user-visible behavior change.

Bug: 77730201
Test: Manually verified as follows:
 1. Open system settings.
 2. Tap "System" -> "Languages & input" -> "Physical keyboard"
 3. Make sure "Show virtual keyboard" is unchecked
 4. Make sure the following command shows 0
      adb shell settings get secure show_ime_with_hard_keyboard
 5. Check "Show virtual keyboard"
 6. Make sure the following command shows 1
      adb shell settings get secure show_ime_with_hard_keyboard
 7. Run the following command
      adb shell settings put secure show_ime_with_hard_keyboard 0
 8. Make sure "Show virtual keyboard" is chenged to unchecked
Change-Id: I956da5dad27313d6edf141f2320bb0a7954fbbea