Change SystemApi as per API council feedback

API council have requested a manifest constant be added
to the SystemApi directly in preference to an indirect
SystemApi constant here:
android.provider.TimeZoneRulesDataContract.READER_PERMISSION.

This is the first of three changes to (1) add the new constant,
(2) switch over code using the constant, (3) remove the
constant.

Bug: 64568899
Test: None, build only
Change-Id: Ib9766591979886d1db3b1d7321536dabf5cf81a8