Add ExplicitHealthCheckService API

The ExplicitHealthCheckService implementation will live in ExtServices
so it can be updated outside of a platform update. It will contain
logic to assist the PackageWatchdog with observing packages, e.g
ensuring that the device can successfully connect to WiFi after a
mainline update.

Test: Builds
Bug: 120598832
Change-Id: If658567ca41bb0328e279735897fc50ab76abc11
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index c7417bf..4150bdd 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -4418,6 +4418,13 @@
     <permission android:name="android.permission.BIND_CARRIER_MESSAGING_CLIENT_SERVICE"
         android:protectionLevel="signature" />
 
+    <!-- Must be required by an {@link android.service.watchdog.ExplicitHealthCheckService} to
+         ensure that only the system can bind to it.
+         @hide This is not a third-party API (intended for OEMs and system apps).
+    -->
+    <permission android:name="android.permission.BIND_EXPLICIT_HEALTH_CHECK_SERVICE"
+        android:protectionLevel="signature|privileged" />
+
     <!-- @hide Permission that allows configuring appops.
      <p>Not for use by third-party applications. -->
     <permission android:name="android.permission.MANAGE_APPOPS"