feat: disposeOnDrag and onTargetHorizontalDragUpdate added

[Kiruel]

Description

Adding disposeOnDrag and onTargetHorizontalDragUpdate to Showcase class.

Checklist

• [x] The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• [x] I have followed the Contributor Guide when preparing my PR.
• [x] I have updated/added tests for ALL new/updated/fixed functionality.
• [x] I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [x] I have updated/added relevant examples in examples or docs.

Breaking Change?

• [ ] Yes, this PR is a breaking change.
• [x] No, this PR is not a breaking change.

[Kiruel]

@vatsaltanna Can you take a look please when you got some times ?

[vatsaltanna]

Sure @Kiruel , Thanks for your PR. Can you please share the reason/use case for this feature ?

[Kiruel]

Yes, working with flutter_slidable when I swap horizontally the showcase do not close. I need to tap. So I add this to handle the drag scroll. Then the user can drag again to open the item. Because when the showcase is started I can't drag the item directly. Maybe they are another solution for it.

[vatsaltanna]

Hi @Kiruel , you can use disableDefaultTargetGestures: true flag to use external target gestures.

[aditya-css]

Hey @Kiruel, Thank you for your contribution. But as @vatsaltanna has mentioned in the previous comment, you can disable the default target gesture and wrap the slidable widget with a GestureDetector and handle the drag there. I am closing this PR because of the above mentioned reason. Feel free to re open if you face any issue with it.