Broadcast PACKAGE_CHANGED in response to OVERLAY_CHANGED

Consolidate what triggers a package change: teach the package manager to
broadcast PACKAGE_CHANGED in response to the overlay manager
broadcasting OVERLAY_CHANGED. Since the overlay manager listens for
PACKAGE_CHANGED, the package manager will include a new extra in the
intent to act as a secret handshake between the managers that the
overlay manager should ignore the intent in order to prevent an endless
loop.

Bug: 140790688
Test: manual (adb shell cmd overlay enable ... && adb shell dumpsys activity broadcasts # check "Historical broadcasts")
Change-Id: I430efcce5adf0dca03058cd6ff694541f0ac3ef5