System API proxies for the telephony module

Introduce classes that exist to give the telephony module something
stable to call for in-process utilities: libcore cannot directly expose
System APIs today and the package names are internal. The APIs are the
subset of internal libcore.timezone APIs used by telephony code
currently.

Bug: 139091367
Test: See associated frameworks/opt/telephony commit
Change-Id: I6109aef77171346ecb103c190526b7b9b81012b2