Turn on transcription when existing dialer user accepts ToS and transcription is available.

Also updated the isVoicemailAvailable helper method, since just checking if the flag and OS is not enough (we have other things such as is VVM enabled, is VM activated), if we don't do this, it doesnt make sense to turn on transcription e.g Why what would happen if transcription is turned on but vvm is disabled

Bug: 74033229
Test: Added a todo, will be added later (there are a few more similar CL's that I am sending for other ToS conditions) to ensure the logic is correct for all ToS conditions first and I can add a test right at the end for all conditions.
PiperOrigin-RevId: 190696695
Change-Id: I9cb063a97e11943abeb1f823dc661efe88dfa3f1