Add phone call handling on the car screen

Incoming calls now show the caller (name via contacts, else number) on
the car UI with answer/decline, using a call screening service so the
car sees a call before it rings. Also adds pinnable nav bar shortcuts,
lowers minSdk to 31 for wider device support, and bumps to 0.0.04-pre.

gearslip/src/main/AndroidManifest.xml

@@ -39,6 +39,18 @@
         android:name="android.permission.WRITE_SECURE_SETTINGS"
         tools:ignore="ProtectedPermissions" />
 
+    <!--
+        Phone calls on the car screen. READ_PHONE_STATE and READ_CALL_LOG together are what a
+        call's own state (ringing, in progress) and the incoming number need; READ_CONTACTS
+        turns that number into a name; ANSWER_PHONE_CALLS lets the driver pick up from here.
+        Declining a call, and the caller ID itself, need Gearslip set as the phone's caller ID
+        and spam app too - an on-device consent, not a permission declared here.
+    -->
+    <uses-permission android:name="android.permission.READ_PHONE_STATE" />
+    <uses-permission android:name="android.permission.READ_CALL_LOG" />
+    <uses-permission android:name="android.permission.READ_CONTACTS" />
+    <uses-permission android:name="android.permission.ANSWER_PHONE_CALLS" />
+
     <!--
       Declared, not just requested. Templated apps decide whether to talk to a host by asking
       whether it holds this permission (HostValidator.isValidHost checks it before falling back
@@ -158,5 +170,21 @@
                 <action android:name="android.service.notification.NotificationListenerService" />
             </intent-filter>
         </service>
+
+        <!--
+          Sees incoming calls before they ring, so the car screen can show the caller and
+          decline it. Inert until the driver sets Gearslip as the phone's caller ID and spam
+          app, under Settings > Apps > Default apps - the same consent a call-blocking app asks
+          for, not a privileged one.
+        -->
+        <service
+            android:name=".call.GearslipCallScreening"
+            android:exported="true"
+            android:label="Gearslip calls"
+            android:permission="android.permission.BIND_SCREENING_SERVICE">
+            <intent-filter>
+                <action android:name="android.telecom.CallScreeningService" />
+            </intent-filter>
+        </service>
     </application>
 </manifest>