AnimationTree State Machine node UX improvements

[Cautami]

This PR includes various UX improvements to how nodes in the AnimationTree's State Machine GUI functions.

Control Dragging

Node dragging via control/command is now properly supported. This feature allows you to click anywhere on a node and begin dragging it, this is primarily useful due to state machine nodes being 90% text.
Prior to this PR, this functionality existed, but the UX on it was lacking.

(note: in both videos I am holding the control key)
Before:

Screencast_20251013_113955.webm

After:

Screencast_20251013_114038.webm

When holding the control key, the cursor IBeam shape and button highlights no longer show, as they aren't functional when control dragging.
You can now re-pick up a node by simply dragging it again, before you had to go through a mandatory deselect
Fixes the selection box appearing despite dragging a node.

Selection Box

Selection box behaviour prior to this PR was weird and inconsistent with how the main blend tree behaved, this PR fixes those issues, and it's behaviour is now consistent with other Node Graph GUIs.

Before:

Screencast_20251013_114233.webm

After:

Screencast_20251013_114302.webm

Shift selection now only removes nodes from the selection.
Control/Command selection now only adds nodes to the selection.

Note: This does remove the ability to invert selection, I don't know if anyone was using this functionality, but given this doesn't exist in the blend tree I found this to be unexpected behaviour.

Additionally, the small flicker that occurs when re-selection happens has been fixed, it's now as smooth as ever.

[Cautami]

I've been thinking about this a bit more, I think the State Machine gui should have a grid like the Blend Tree gui does.
That being said, I don't think that's within the scope of this issue, but I am wondering if I should move ctrl dragging to the alt key instead, in the blend tree holding ctrl deals with the grid, if we moved ctrl dragging in the state machine to alt we could also have this be a thing in the blend tree aswell, giving them both better parity, this would also align it with other node graphs, like Material Maker (the program), which does what I'm suggesting here.

[Cautami]

Sorry! I think I totally messed up the git history by accident, should be fixed now?