feat(gestures): pan gesture start position support - #11435

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• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
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• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

Right now, pan gesture does not expose the initial touch position in the event listener.

What is the new behavior?

This PR adds startX and startY in the pan gesture event data.

Few additions:

• Corrected PinchGestureEventData class that was implementing itself
• Added CustomGestureDetector internal class for pan and rotate to extend