Adding Skeleton Code for Customizable Taksbar

This cl includes
        - new skeleton xml view customizable taskbar view
        - new skeleton xml view for customizable taksbar container and a view class.
        - new taskbar all apps button view container class
        - pxFromDp util method introduction to launcher utilities

Test: Presubmit
Bug: 349885828
Bug: 349886203
Flag: com.android.launcher3.enable_taskbar_customization
Change-Id: Id83906ed0717da495c33275e52261153a1598074