Annotate Data and Voice Roaming setters with @TestApi.

CTS testing for ServiceState's getRoaming() requires using
setDataRoamingType() and setVoiceRoamingType() for preparing state.
These are currently annotated as @hide and @UnsupportedAppUsage, with a
maxTargetSdk of P.

Bug: 74207290
Test: atest CtsTelephonyTestCases:ServiceStateTest
Change-Id: I08efeeae81494c0431ce34c5d68a73d4824c8d1d