Create app icon entry point

Adjusted grid entry point title and created basic icon entry point,
currently without thumbnail or subtitle.

Flag: com.android.systemui.shared.new_customization_picker_ui
Bug: 402161932
Test: manually verified
Test: AppIconViewModelTest passes
Change-Id: Ibc94c18695a0c491f0d6408f9faa6811017b2a7e