text: Take the gutter into account when masking text

Flash Player does not render text over the gutter.

Author: kjarosh

core/src/display_object/edit_text.rs

@@ -2702,7 +2702,10 @@ impl<'gc> TDisplayObject<'gc> for EditText<'gc> {
         }
 
         context.commands.push_mask();
-        let mask = Matrix::create_box_from_rectangle(&self.0.bounds.get());
+
+        let mask_bounds = self.0.bounds.get().grow_x(-Self::GUTTER);
+        let mask = Matrix::create_box_from_rectangle(&mask_bounds);
+
         context.commands.draw_rect(
             Color::WHITE,
             context.transform_stack.transform().matrix * mask,

swf/src/types/rectangle.rs

@@ -165,6 +165,15 @@ impl<T: Coordinate> Rectangle<T> {
         self
     }
 
+    #[must_use]
+    pub fn grow_x(mut self, amount: T) -> Self {
+        if self.is_valid() {
+            self.x_min -= amount;
+            self.x_max += amount;
+        }
+        self
+    }
+
     #[must_use]
     pub fn is_point(&self) -> bool {
         self.x_min == self.x_max && self.y_min == self.y_max