* DragTarget part 1.

[WIP] Change GestureRecognizer. Sorry.

[WIP] Move from GestureRecognizer to MultiDragGestureRecognizer.

Make it a `Set<int>?`

Get bitwise operations working.

Fix test. Rename to allowedInputPointers.

Convert into a builder.

Improve code with default funciton.

Refactor everything again.

Rename to buttonEventFilter.

Use static function.

Fix analyzer.

Fix private reference.

Use // in private method.

* Fix Renzo request.

* Add `allowedButtonsFilter` everywhere.

* Refactor monoDrag for multi pointer support.

* Fix tests?

* Change default to always true.

* Fix PR comments.

* Completely refactor long press.

* Add forgotten class.

* Revert "Completely refactor long press."

This reverts commit 5038e8603e250e8c928b0f1754fb794b7b75738b.

* Add default value to LongPress

* Refactor doubleTap.

* Relax double tap.

* Write comment in LongPress.

* Use template.