[Physical Keyboard][A11y Page] Add custom slider

add slider for setting custom value under bounce key dialog.

demo video: b/346949547#comment26

Bug: 346949547
Test: atest SettingsRoboTests
Flag: com.android.settings.keyboard.keyboard_and_touchpad_a11y_new_page_enabled
Change-Id: I3b7f08ebe5ebc287e61713749c193c8b1cf71b99