core: Make objects focusable by default

Since is_focusable has been moved to InteractiveObject,
it may now return true by default, because non-interactive objects
do not implement this method anymore.

core/src/display_object/avm1_button.rs

@@ -624,10 +624,6 @@ impl<'gc> TInteractiveObject<'gc> for Avm1Button<'gc> {
         }
     }
 
-    fn is_focusable(&self, _context: &mut UpdateContext<'_, 'gc>) -> bool {
-        true
-    }
-
     fn on_focus_changed(
         &self,
         context: &mut UpdateContext<'_, 'gc>,

core/src/display_object/avm2_button.rs

@@ -824,10 +824,6 @@ impl<'gc> TInteractiveObject<'gc> for Avm2Button<'gc> {
         }
     }
 
-    fn is_focusable(&self, _context: &mut UpdateContext<'_, 'gc>) -> bool {
-        true
-    }
-
     fn on_focus_changed(
         &self,
         _context: &mut UpdateContext<'_, 'gc>,

core/src/display_object/edit_text.rs

@@ -2471,11 +2471,6 @@ impl<'gc> TInteractiveObject<'gc> for EditText<'gc> {
         }
     }
 
-    fn is_focusable(&self, _context: &mut UpdateContext<'_, 'gc>) -> bool {
-        // Even if this isn't selectable or editable, a script can focus on it manually.
-        true
-    }
-
     fn on_focus_changed(
         &self,
         context: &mut UpdateContext<'_, 'gc>,

core/src/display_object/interactive.rs

@@ -511,9 +511,10 @@ pub trait TInteractiveObject<'gc>:
         MouseCursor::Hand
     }
 
-    /// Whether this clip may be focusable for keyboard input.
+    /// Whether this object is focusable for keyboard input.
     fn is_focusable(&self, _context: &mut UpdateContext<'_, 'gc>) -> bool {
-        false
+        // By default, all interactive objects are focusable.
+        true
     }
 
     /// Called whenever the focus tracker has deemed this display object worthy, or no longer worthy,