Fix ANR in WifiCallingPreferenceController.getAvailabilityStatus

Move the following to background thread to avoid block main thread,
- MobileNetworkUtils.isWifiCallingEnabled(mContext, mSubId, null)
- MobileNetworkUtils.buildPhoneAccountConfigureIntent()
- getSummaryForWfcMode()
- Call State

Since WifiCallingPreferenceController no longer calculate availability
in getAvailabilityStatus(), also update the
CallingPreferenceCategoryController accordingly.

Also introduce ImsMmTelRepository for split business logic for easy
testing.

Fix: 292401934
Test: manual - on Mobile Settings
Test: unit test
Change-Id: If92e2c8f6e137e40b83e578294c03c1b917eef8e