OrbitControls: fix zoom-changed detection

[sciecode]

Fixes #27831

At some point our logic for detecting zoomChanged was modified and it is currently not functioning properly. Currently, the changes are being detected by the condition that validates camera movement and not actual zoom, however this is unreliable as seen in the linked issue.

I made sure to properly detect changes for every variation of zoom logic (ortho/persp for zoomToCursor and regular zoom).

Also took the opportunity to only set this variable if zoom was actually modified, and not every time it is attempted. This way, if the zoom event is triggered but camera is already clamped to min/max distance, an event won't be triggered falsely.

[sciecode]

Just validating a few edge cases to make sure everything is working properly, will merge soon.

[sciecode]

Everything appears to be functioning properly.

https://jsfiddle.net/dhqg9f8x/ (ortho)
https://jsfiddle.net/wdpLc4xk/ (persp)