Adjust transform plane positions based on camera orientation

[Oblepikha]

Fixes godotengine/godot-proposals#7358

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[Oblepikha]

Fixed weird behavior when a gizmo is near the edge of the screen

[Oblepikha]

Disabled in orthographic view. Do not move planes while a transform operation is in progress (dragging or scaling)

[Oblepikha]

I rewrote the way move and scale handles are selected. They are now approximated with spheres, projected onto the screen, and evaluated based on their distance to the mouse cursor. This makes it possible to select occluded handles

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I also slightly increased the size of the transform planes. Hopefully no one has any objections 😅

[passivestar]

Tested, works as expected, UX makes sense, didn't look at the code

[Oblepikha]

Merge conflicts resolved

[YeldhamDev]

Please end the new comments with a period.

[Oblepikha]

Updated the comments.

[Oblepikha]

Implemented the center controls proposed in godot-proposals/issues/14563

[Mickeon]

Hold on. The PR is going way out-of-scope of what was originally intended. I would recommend sticking to one thing at the time, and opening separate PRs for each feature/fix. The PR's title and commit name do not even match what is being done anymore.

Please just stick to what was approved of last time.

[Oblepikha]

Yeah, fair point. I started working on it and got carried away. I've reverted the latest changes and moved them into a separate PR