Use isMobileDataCapable helper in network/datausage components

Disabling telephony support may be done either with the
config_show_sim_info config option, or based on whether
TelephonyManager reports data capabilities. The isMobileDataCapable()
helper method ensures both ways are supported.

Most of the logic in the data usage components rely on a
DataUsageUtils.hasMobileData(), which is already equivalent to
!Utils.isWifiOnly(), i.e. looking at the TelephonyManager mobile data
support. Instead of removing all uses of hasMobileData(), the method
itself has been updated to rely on the new isMobileDataCapable()
helper, so that all the unit tests that mocked hasMobileData() don't
need to be updated.

The relevant unit tests are also updated to mock TelephonyManager
directly.

Bug: 395714454
Test: atest tests/robotests/src/com/android/settings/datausage/
Test: atest tests/spa_unit/src/com/android/settings/datausage/
Flag: EXEMPT bugfix
Change-Id: I722e25ea7b0b078d006ff027e721dd1bc95da17a