Add isMobileDataEnabled in TelephonyManager.

Added a new hidden API isMobileDataEnabled in TelephonyManager.
Rename related APIs to isUserMobileDataEnabled,
isUserMobileDataEnabled and setUserMobileDataEnabled to better
clarify their functionality.

Bug: 69814555
Test: build
Change-Id: I2f186f1e7550cafbe4ee3a5af293c39274cbfeaa
Merged-In: I2f186f1e7550cafbe4ee3a5af293c39274cbfeaa