Disable entries in CallingAccountSelector that are not selectable

This CL also unifies the disabled color for primary and secondary text.

The in call UI dialog will be implemented in a followup CL.

TEST=TAP
DEFAULT_VALUE_OK=no server.
Bug: 69675796,72618783
Test: TAP
PiperOrigin-RevId: 194147061
Change-Id: I5be5a45a7df09061a3bf391f6ae2a32d9c73b6e3