Add availabilityProvider attribute for roles.

This change adds a new availabilityProvider attribute for roles, thus
allowing the dialer and SMS role availability to work as before.

Bug: 110557011
Test: build
Change-Id: I03b7ba56189f549fb2326582e43628dbc9beebdf
diff --git a/PermissionController/proguard.flags b/PermissionController/proguard.flags
index 46a929e..05defe9 100644
--- a/PermissionController/proguard.flags
+++ b/PermissionController/proguard.flags
@@ -6,3 +6,8 @@
     *;
 }
 -dontwarn androidx.core.**
+
+# Keep classes that implements RoleAvailabilityProvider, which are used by reflection.
+-keep class * implements com.android.packageinstaller.role.model.RoleAvailabilityProvider {
+    *;
+}