Adds a Hilt module for test dependencies

See go/picker-test-injection

Bug: b/297021618
Test: verified that tests use deps from test module
Change-Id: Iada1f20cd69d3e7ce3d80eae3bfdfa5edc57e821
diff --git a/Android.bp b/Android.bp
index 9f7dbdb..d3a7c51 100644
--- a/Android.bp
+++ b/Android.bp
@@ -35,6 +35,13 @@
     ],
 }
 
+// Production-only files that should be excluded in tests.
+filegroup {
+    name: "ThemePicker_src_prod",
+    visibility: [":__subpackages__"],
+    srcs: ["src_override/com/android/customization/picker/CustomizationPickerApplication.java"],
+}
+
 filegroup {
     name: "ThemePicker_Manifest",
     srcs: [