UX and stability improvements for Path3D node

[GreenCrowDev]

UX and stability improvements for Path3D node.

Goals are:

• Declutter the UI showing only the appropriate handles in the respective modes;
• Solving issues caused by subgizmos overlapping each other.

Closes #89138
Closes #85795
Closes #88276 offering a "cleaner" solution
Closes godotengine/godot-proposals#8890

TODOs:

• Show transform gizmo only when in Select Points mode;
• Show secondary handles only when in Select Control Points mode;
• Clear subgizmo selection when changing mode;
• Add a Select Tilt Points mode that only shows tilt disks.

Toolbar with the new Select Tilt Points mode:

Select Points mode is cleaner (the only thing is missing is changing the color of the selected control points, eventually suggest in which part of the code this change should be made, I couldn't get it in a straightforward way):

2024-03-25-16-07-59.mp4

Select Control Points shows the secondary handles. This mode permits moving points freely. If you need to "drag out" the points from their default position, you have to press shift (the tooltip text explains that):

2024-03-25-16-08-25.mp4

Select Tilt Points is the new mode that shows the tilt disks and handles, decluttering the other modes and solving other issues (tilt handles and secondary handles where often in conflict):

2024-03-25-16-08-47.mp4

[fire]

I'm heading back from a convention, but I'll love to review in a few. Will try to find a few others.

[fire]

@Calinou I'd really appreciate if you take a look?

[fire]

I like the usability improvements for Path3D feature wise. I did not review the code at depth.

For example:

Split the two types of "extra" handles like shape and disc helps reduce the difficult in using Path3D. Also the shift idea sounds good.

There's a process for optimizing svg, but it can be done in a later pr. https://docs.godotengine.org/en/3.6/development/editor/creating_icons.html

[GreenCrowDev]

I'm pretty sure I already optimized the SVG following that guide (could I have it done wrong?) 🤔
Thanks for the review!

[Calinou]

Tested locally (rebased on top of master 29b3d9e), it works as expected.

There are future improvements we could make (these usability issues also existed in master):

• You can't drag a point relative to the current view in Select Points mode. You can only do that in Select Control Points or Select Tilt Handles modes.
• You can't create a new handle out of a point by holding Shift then dragging a point in the Select Points mode. Again, this only works in the Select Control Points or Select Tilt Handles modes.

Both of the above could be implemented using a drag distance threshold, where dragging by 8 * EDSCALE pixels or more would be considered a dragging operation, and dragging a lower distance before releasing the mouse would be considered a selection operation.

• Handle tilts could be displayed as degrees in the bottom-left corner when dragging one:

For reference, this is what the Node3D rotation gizmo message looks like:

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉