[Physical Keyboard] Show correct format in a11y key dialog

Format decimals in dialog to avoid inconsistent through languages.

Bug: 388330691
Test: atest SettingsRoboTests
Flag: com.android.settings.keyboard.keyboard_and_touchpad_a11y_new_page_enabled
Change-Id: Icbf1eec2b31614768efb079f4cbeec1fd5b73ef5