Add device and carrier flags for video calling fallback

These flags let the system dialer/contacts/SMS app determine if
integration with video calling apps are allowed if the carrier video
calling is not available.

EXTRA_SUPPORTS_VIDEO_CALLING_FALLBACK in PhoneAccount.getExtras()
should be checked first. This flag is disabled by default and OEMs
will need to enable it.

If the device supports the fallback, then
CarrierConfigManager.KEY_ALLOW_VIDEO_CALLING_FALLBACK_BOOL should be
checked so individual carriers can ban the feature. This flag is
allowed by default.

Change-Id: Id46f684254402acb9142f87684ddff2d830f1701
Fixes: 62264468
Test: manual
diff --git a/telecomm/java/android/telecom/PhoneAccount.java b/telecomm/java/android/telecom/PhoneAccount.java
index b5d9d393..4390fae 100644
--- a/telecomm/java/android/telecom/PhoneAccount.java
+++ b/telecomm/java/android/telecom/PhoneAccount.java
@@ -92,6 +92,18 @@
 
     /**
      * Boolean {@link PhoneAccount} extras key (see {@link PhoneAccount#getExtras()}) which
+     * indicates whether this {@link PhoneAccount} supports using a fallback if video calling is
+     * not available. This extra is for device level support, {@link
+     * android.telephony.CarrierConfigManager#KEY_ALLOW_VIDEO_CALLING_FALLBACK_BOOL} should also
+     * be checked to ensure it is not disabled by individual carrier.
+     *
+     * @hide
+     */
+    public static final String EXTRA_SUPPORTS_VIDEO_CALLING_FALLBACK =
+            "android.telecom.extra.SUPPORTS_VIDEO_CALLING_FALLBACK";
+
+    /**
+     * Boolean {@link PhoneAccount} extras key (see {@link PhoneAccount#getExtras()}) which
      * indicates whether this {@link PhoneAccount} is capable of supporting a request to handover a
      * connection from this {@link PhoneAccount} to another {@link PhoneAccount}.
      * (see {@link android.telecom.Call#EVENT_REQUEST_HANDOVER}) which specifies