Toast on broadcast receiver notification trampolines

Show a warning toast when an app starts an activity inside a broadcast
receiver in response to a notification or notification action click.
This is to gather dogfood feedback in preparation for blocking such
activity starts. See go/notification-trampolines for more info. For now,
only taking care of broadcast receivers, the services case will be in a
future CL.

The toast is only shown once per package. This is to avoid annoying
dogfooders.

The actual block will be gated on targetSdk, however since very few
apps (any?) will be targeting the latest SDK on dogfood and we are still
allowing the activity start, we're going to show a toast regardless of
targetSdk to collect more feedback.

A side-effect of the way we implemented the rule that allowed
notification trampolines in BAL is that in the case that the user clicks
on a broadcast/service-trampoline notification of an app that also
happens to be in the foreground (on top for example) we can't
differentiate if an activity start came from the broadcast/service or
from the activity itself (or some other part of the app). Because of
this, in this case, we won't show the warning toast (and I'd say we
might not block the launch in the future, but this discussion can wait).

Implementation:

We determine at PendingIntent fire time if the receiver is allowed to
start activities. However, we pass a boolean to represent the grant to
start activities and this boolean also takes into account another case
that allows such starts. To correctly identify at activity start time
that it was allowed due to notification-click scenario we pass in the
token that was embeded in the PendingIntent (and was validated in the
PendingIntentRecord) by notification manager.

The set of components in ProcessRecord becomes a map to contain the
originating tokens. Since now WindowProcessController needs to have the
token to trace back the grant, I've replaced the boolean flag with the
map from ProcessRecord. We move the grant rule to the bottom of the
method areBackgroundActivityStartsAllowed() to make sure the start was
allowed exclusively due to notification-click interaction.

We then let notification manager register a callback with activity task
manager that will be called whenever a background activity start is
allowed exclusively due to a token provided in that callback. In that
callback we show the warning toast.

Test: atest BroadcastRecordTest BackgroundActivityLaunchTest
      ActivityStartControllerTests ActivityStarterTests
      RecentsAnimationTest WindowProcessControllerMapTests
      WindowProcessControllerMapTests
Test: Posted a broadcast-trampoline notification, clicked on it and
      observed the toast was shown.
Change-Id: Ica479d7d2f6b5f2ddaac4c59e12d0b25cd637717