Backport missing permission check for querying main activity intent

- This was fixed in T in ag/16820166, but the original code was
  submitted in S.  This ensures that the caller of this method
  is either holding the ACCESS_SHORTCUTS permission or is the
  default launcher.

Bug: 229256049
Test: atest WMShellUnitTests

Change-Id: Ib233ad754a6c6e3c4e0d0e10ed788ab8e055cccc
Merged-In: Ib233ad754a6c6e3c4e0d0e10ed788ab8e055cccc
(cherry picked from commit f4ed441e)