Expose RoleManager#getDefaultSmsPackage

Expose this method for module libraries. It's needed to support a public
method in TelephonyProvider that doesn't require any permissions.

Test: atest RoleManagerTest#smsRoleHolderAvailableWithoutObserveRoleHolders
Fixes: 169350676
Change-Id: Ia2725dc5aa0de74b2cf67ecd0666917ae27adda9