Refactor AppPicker to adopt the latest UX

- get rid of ListActivity
- add aconfig

Bug: 299195099
Test: manual
Change-Id: I922ffb46f3132d117b0f682d8076f9e975d02b2c

aconfig/Android.bp

@@ -47,3 +47,16 @@ java_aconfig_library {
     name: "accessibility_settings_flags_lib",
     aconfig_declarations: "accessibility_flags",
 }
+
+aconfig_declarations {
+    name: "development_settings_flags",
+    package: "com.android.settings.development",
+    srcs: [
+        "development/**/*.aconfig"
+    ],
+}
+
+java_aconfig_library {
+    name: "development_settings_flag_lib",
+    aconfig_declarations: "development_settings_flags",
+}