Use RequiresApi instead of TargetApi in NotificationManager

[rvandermeulen]

AGP 8.9.0 is tightening up the lint checks around TargetApi/RequiresApi. With the most recent alpha04 build, we see the following error:

/reference-browser/app/src/main/java/org/mozilla/reference/browser/NotificationManager.kt:181: Error: Use @RequiresApi(Build.VERSION_CODES.O) instead of @TargetApi` to propagate the requirement to callers of createNotificationChannelIfNeeded [UseRequiresApi]
    @TargetApi(Build.VERSION_CODES.O)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

   Explanation for issues of type "UseRequiresApi":
   The @TargetApi annotation only suppresses API warnings locally.
   @RequiresApi on the other hand will propagate the requirement out to any
   callers of this API, making sure that they either perform API level checks
   (using for example SDK_INT), or defining @RequiresApi annotations
   themselves.

   (The @TargetApi annotation predates @RequiresApi, and was introduced as an
   early way to suppress lint API warnings for a particular API level.
   Accidentally using @TargetApi can lead to crashes since there is no check
   that other calls to this method actually check that the call is safe.)

[rvandermeulen]

And yes, m-c is going to require some similar changes.

[jonalmeida]

Thanks for answering my question before letting me ask it. 😄