This fixes a few issues with the "Mobile network" preference that shows
on the Network & internet page:
-The pref should not be available at all if the device is wifi-only.
-The pref should be disabled in airplane mode.
-If eSIM support is disabled, we need to disable entry points for adding
a new eSIM subscription (the summary and click handler in single-SIM
mode with no physical SIM, and the 'add' button in dual-SIM mode).
Bug: 116349402
Test: make RunSettingsRoboTests
Change-Id: Ic6fe426e9f890d80b399d48a2c9984d4d8b02a10
475dde51b6