Update shortcuts to match spec

Necessary information for a shortcut is label, icon, intent. This alters
how that information is retrieved from a Slice and falls back to using
the app icon / title / intent if any of the information is missing from
the slice ensuring that there is always an actionable shortcut.

Also adds notion of HINT_HIDDEN, allowing apps to exclude parts of a slice
from being visible in a template, note when creating a shortcut HINT_HIDDEN
is ignored.

Test: Manual with SlicesApp, test different varients of having HINT_TITLE
      and not having HINT_TITLE on an action / icon / label as well as
      not having an icon / label / or action.
Bug: 68378574

Change-Id: I1de9e502204dfb7fd83a7ec7622e8fd464146cfd