Migrate ENABLE_RESPONSIVE_WORKSPACE to aconfig

- Keeping FeatureFlags.ENABLE_RESPONSIVE_WORKSPACE for local testing until aconfig is available in FlagFlipper
- Still reference ENABLE_RESPONSIVE_WORKSPACE in tests as aconfig still can't be mocked

Bug: 299935275
Test: manual
Change-Id: I092df894a3624dca6b9d381d56ada71d807547b5
diff --git a/aconfig/launcher.aconfig b/aconfig/launcher.aconfig
index b4132e4..9221f6b 100644
--- a/aconfig/launcher.aconfig
+++ b/aconfig/launcher.aconfig
@@ -27,3 +27,10 @@
     description: "Enables cursor hover states for certain elements."
     bug: "243191650"
 }
+
+flag {
+    name: "enable_responsive_workspace"
+    namespace: "launcher"
+    description: "Enables new workspace grid calculations method."
+    bug: "241386436"
+}