Create a new stateful widget called
FilterSelector that you’ll use to 
implement the selector.

Add the FilterSelector widget to the existing
widget tree. Position the FilterSelector widget
on top of the photo, at the bottom and centered.

Within the FilterSelector widget,
display a selector ring on top of a 
dark gradient by using a Stack widget.

The size of the selector circle and the background gradient
depends on the size of an individual filter in the carousel
called itemSize. The itemSize depends on the available width.
Therefore, a LayoutBuilder widget is used to determine the
available space, and then you calculate the size of an 
individual filter’s itemSize.

The selector ring includes an IgnorePointer widget
because when carousel interactivity is added,
the selector ring shouldn’t interfere with 
tap and drag events.

Create a filter carousel item