Introduce developer option for Stylus handwriting

Introduce a new developer option for Input Method:
Stylus handwriting: when this setting is enabled, currently selected
input method receives stylus events after focus on editor.

Bug: 219777744
Test: atest StylusHandwritingPreferenceControllerTest
Change-Id: Ia6335df60aae56973ed54bec1a243ea1de3aa6ad

src/com/android/settings/development/DevelopmentSettingsDashboardFragment.java

@@ -582,6 +582,7 @@ public class DevelopmentSettingsDashboardFragment extends RestrictedDashboardFra
                 bluetoothA2dpConfigStore, fragment));
         controllers.add(new SharedDataPreferenceController(context));
         controllers.add(new OverlaySettingsPreferenceController(context));
+        controllers.add(new StylusHandwritingPreferenceController(context));
 
         return controllers;
     }