Fixed some issues with alert window notifications

- Don't hold window manager lock while calling into notification
manager since it can end up calling into activity manager.
- Fixed issue with using checkCallingPermission() to check if the
system has the internal system window permission. This call fails
if it isn't a binder call. Change to use checkCallingorSelfPermission()
instead.
- Fixed class cast exception while getting app icon by using
IconUtilities class to the the drawable to bitmap convertion.

Change-Id: I4ef380618f558a8aac5b152d97536a614040397f
Fixes: 35780846
Fixes: 35846667
Fixes: 35854470
Bug: 35657567
Test: cts/hostsidetests/.../run-test CtsWindowManagerHostTestCases android.server.cts.AlertWindowsTests