Add molding segments to the Path tool

[4adex]

Part of #1870:

• Clicking and dragging without any modifier key, as per Sculpting / molding segments with the Path tool #615, should mold the segment.

Closes #615.

[Keavon]

!build

[github-actions]

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https://f7febd05.graphite.pages.dev

[Keavon]

• Right-click and Escape need to work to cancel molding
• Alt should temporarily break colinearity and mold only the dragged segment, while also snapping the handles back to where they began before the molding drag began
• C should permanently toggle colinearity on the two adjacent anchors, without snapping the handles back like above (be sure to handle the case where they're each initially of opposite state)
• Hints should be updated for all of the above
• We can merge this but then move onto finding a better algorithm that suits our desired molding behavior better
• Please don't put any new code into Bezier-rs, find somewhere reasonable in the editor code to put that. Thanks.