Add cancel button to Erase all data (factory reset)

Bug: 300634367
Test: unit test & manual test
Change-Id: I860955291b27ea1f7c748ac746b91153224eacb7

aconfig/settings_flag_declarations.aconfig

@@ -0,0 +1,8 @@
+package: "com.android.settings.flags"
+
+flag {
+    name: "show_factory_reset_cancel_button"
+    namespace: "android_settings"
+    description: "This flag controls whether to show a Cancel button when factory reset"
+    bug: "300634367"
+}