Allow system dialer to use phone call FGS.

The OEM dialer should be allowed to start a phone call FGS even if it
does not hold ROLE_DIALER role.  The user may have chosen another app
to be their dialer app, however when the user places an emergency call
we will always fall back to the OEM dialer.  The OEM dialer is also
used as a fallback in the case where a user's chosen dialer crashes during
a call as it is seen as a more stable alternative to provide call control.

Fixes: 425971621
Flag: android.app.system_dialer_phone_call_fgs_grant
Test: Added testForegroundServiceTypePhoneCallSystemDialer CTS test.
Change-Id: I444d9e233d355751282abc9da7650f7fe7c6e3a5