Added Dialog for Shortcut Customization

Created view model, interactor and UI for shortcut customization in
shortcut helper.

Fix: 373621697
Flag: com.android.systemui.keyboard_shortcut_helper_shortcut_customizer
Test: Enter shortcut customization mode in shortcut helper, click the
add icon on a shortcut, ensure that add shortcut dialog pops up

Change-Id: Ib93936517ea7241a1f406d3e509a066e5180ae5d