Fix Drag/Release Behavior in GUI and Photo Dome

[stevendelapena]

See: https://forum.babylonjs.com/t/ispointerblocker-improvement/31152/10?u=stevendelapena

Recent changes to GUI mouse behavior breaks previous behavior for scenes utilizing a Video and Photo Domes. See PG: https://playground.babylonjs.com/#SQ5UC1#375 and https://playground.babylonjs.com/#14KRGG#715

Click and drag from outside of GUI element to gain control of camera. Release mouse from within the GUI element. You’ll notice the camera is still observing the mouse movement and pans around with mouse even though click/pointer has been released

Fix suggested is to allow mouse release to propagate to scene to allow for release of camera observers.

[azure-pipelines]

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[azure-pipelines]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[azure-pipelines]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[azure-pipelines]

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[OPSnake]

I have same problem in my app and it's solved with your fix 👍

[PolygonalSun]

LGTM

[carolhmj]

Thanks for the fix! :D