feat: taps should pass through when onTap is unset

[AndersKlint]

Issue

Fixes: Feature Request: TransformableBox should enable onTap Event Propagation to Child Widgets #31

Problem statement

Currently the TransformableBox captures all tap events and forwards them to the onTap callback. This becomes problematic if we want the content of the TransformableBox to capture onTap events (or whatever is rendered behind the box, in case the content is ignoring pointer events).

Testing

Manual testing have been performed with the following setup:

// pseudo  code
stack: [
  GeastureDetector(
    onTap: _onTap,
    child: CameraPreview()
  ), 
  TransformableBox(
     // ... //
     tapThrough: true,
      },
      contentBuilder: (context, rect, flip) => IgnorePointer(
        child: DecoratedBox(
          decoration: BoxDecoration(
            border: Border.all(
              width: 2,
            ),
          ),
        ),
      ),
    );
]

• When the onTap arg was provided, the tap event was captured by the TransformableBox.
• When the onTap arg was not provided, the tap event was captured by the CameraPreview's GestureDetector.

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docs.page/hyper-designed/box_transform~32

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