Expose SmsManager#sendTextMessageWithoutPersisting as a public API

This API is useful for carrier-privileged apps that wish to use SMS to
transmit carrier system messages without affecting the user-visible
message database.

Change-Id: Ie4f765f3f42a942f5d6d9c85513dc9abaaf32962
Fixes: 25563895
Test: No functional changes.  CTS test
SmsManagerTest#testSmsNotPersisted_failsWithoutCarrierPermissions added
that asserts a failure because CTS does not have carrier permissions