Add receiver flag enforcement workaround for apps targeting U

Android T allows apps to declare a runtime receiver as not exported
by invoking registerReceiver with a new RECEIVER_NOT_EXPORTED flag;
receivers registered with this flag will only receive broadcasts from
the platform and the app itself. However to ensure developers can
properly protect their receivers, all apps targeting U or later
registering a receiver for non-system broadcasts must specify either
the exported or not exported flag when invoking #registerReceiver;
if one of these flags is not provided, the platform will throw a
SecurityException. Some apps have already begun targeting U but
have not yet flagged their exposed receivers; this commit adds an
exemption for these apps to prevent them from crashing due to this
new enforcement while their receivers are updated.

Bug: 258849947
Test: Manually verified affected packages did not crash with enforcement
Change-Id: Iaa5b48f874e3aa9657b2dfd9fd2e34fe782a5a23