Curve editor multiselect drag correctly clamped when out of bounds

[LeDernierPoisson]

Pull Request

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Summary

Changes how the curve editor handles dragging multiple keyframes out of the range.

Previously , when having multiple keyframes selected and dragging them together, if you would hit the ranges bound with some keyframes they would get clamped and all the other would continue to move. Now if you do that all the keyframes will be clamped as soon as one keyframe in the selection is getting out of bounds

Motivation & Context

The old behaviour was really a pain in the ass and made me stop using this feature at all.
The principle reason is that I would often "break" the shape of the selected keyframes when i wanted to drag near the bounds. Coupled to the fact we don't have undo's and redo's on this widget it made for a really destructive feature ,especially when you wanted to move a big selection of keyframes.

Screenshots / Videos (if applicable)

Before

Curve-Multiselect-Before-Fix.mp4

After

Curve-Multiselect-After-Ix.mp4

Checklist

• Code follows existing style and conventions
• No unnecessary formatting or unrelated changes
• Public APIs are documented (if applicable)
• Unit tests added where applicable and all passing
• I’m okay with this PR being rejected or requested to change 🙂