Add a `released` event to widget Responses

**Is your feature request related to a problem? Please describe.**

I want to be able to drag and drop files inside a widget (like TextEdit for example) but the thing is currently there is no way to find out if the dragged files released inside a specific widget. I tried to use `is_pointer_button_down_on` for this job, but this function only return true if button pressed/released when hovering on the widget (in other word if I drag a file at top of a widget then release mouse button to drop it, it dont receive any release event...), so I think a `released` Response that return true when ever a button released at top of it would be good.

**Describe the solution you'd like**

Having a new function named `released` that return `true` when a button released at top of widget.

**Describe alternatives you've considered**

change `is_pointer_button_down_on` functionality in order to return true in case that a button released at top of it (and not just when it first hovered on it) although I don't think its a good Idea... having a specific function would be better.

**Additional context**

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Start by tracing the existing `is_pointer_button_down_on` response handling and related widget pointer-event entry points. Verify the proposed `released` response for releasing a dragged file or button over a widget; the issue provides no file or test path.

Written by the indexing model from the issue text.