Don't show incoming SMS notification for blocked numbers when user is locked.

Also ensure that messages are not permanently dropped due to being blocked
until they can be processed again when the credential-encrypted storage is
available (unless they are handled by a filter further down the chain, e.g.
visual voicemail).

Add unit tests to exercise the notification for both blocked and unblocked numbers.

Bug: 156910035
Test: atest GsmInboundSmsHandlerTest; on-device test of blocked SMS
Change-Id: Ie3798fcbbc44fc8b7893a3cdf709ad1825519a85