Add flags for switching RE to Vulkan and Graphite

We are working towards shipping RenderEngine using Skia's Graphite
Vulkan backend, so add a flag for that. In addition, add a flag for
switching RenderEngine to use Vulkan while still using Skia's older
Ganesh backend. This will allow us to get more soak time with Vulkan
while we get Graphite working here.

Bug: 293371537
Test: NA
Change-Id: Id1e8db7a33b8dbffb9e713bd2d8afa4ca5dbf8a9
diff --git a/services/surfaceflinger/surfaceflinger_flags.aconfig b/services/surfaceflinger/surfaceflinger_flags.aconfig
index b65a2b3..42249ac 100644
--- a/services/surfaceflinger/surfaceflinger_flags.aconfig
+++ b/services/surfaceflinger/surfaceflinger_flags.aconfig
@@ -149,3 +149,19 @@
   bug: "286084594"
   is_fixed_read_only: true
 }
+
+flag {
+  name: "vulkan_renderengine"
+  namespace: "core_graphics"
+  description: "Use Vulkan backend in RenderEngine prior to switching to Graphite."
+  bug: "293371537"
+  is_fixed_read_only: true
+}
+
+flag {
+  name: "graphite_renderengine"
+  namespace: "core_graphics"
+  description: "Use Skia's Graphite Vulkan backend in RenderEngine."
+  bug: "293371537"
+  is_fixed_read_only: true
+}