Updating telephony to use flags to mark dynamically registered receivers

as exported or not exported to comply with ag/15099757.
All flags are hidden behind testing/debug flags, so marking as exported. Effectively a no-op.

Test: no changes to CTS necessary, seems like many existing tests are already broken per https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/opt/telephony/+/15881627
Change-Id: I8e5d8af4e8cc6617fd3a2b55a4adfc6933eef4f0
Bug: 161145287