Disable flights during morph

[bagnell]

• Run the Sandcastle camera example
• Switch to CV. Try to click "Fly to My Location" during the morph.
• Switch to 2D. The globe will disappear during the morph. This does not happen if we don't click "Fly to My Location."

[hpinkos]

Instead of the globe disappearing, a developer error is thrown if you try to fly during a morph:

Uncaught DeveloperError: lookAtTransform is not supported while morphing.

Can we close this?

[pjcozzi]

Can we fix the Sandcastle example to disable the flight while morphing?

[hpinkos]

Just kidding, this is actually still an issue.
In the camera example remove line 258
viewer.camera.lookAtTransform(Cesium.Matrix4.IDENTITY);

That's what was causing the crash.

[pjcozzi]

@hpinkos should we keep this open after #4496?

[hpinkos]

@pjcozzi #4496 made it so the sandcastle example won't crash, but I feel like we should probably make changes to Camera.flyTo should wait until the scene morph finishes before creating the CameraFlightPath. So I think this should stay open