Tracking Issue: Improving editing support for vector meshes

[4adex]

This issue tracks existing bugs related to the Pen Tool and Path Tool when working with vector meshes, especially in scenarios where an anchor point is connected to more than two segments. Many existing features assume that anchors are only shared by at most two segments, which breaks certain behaviours when this assumption is violated.

• [ ] Pressing C while dragging a handle from an anchor point does not work well when more than two segments are connected to the corresponding anchor. (For both path tool and pen tool).
• [ ] Alt + drag while a handle is selected makes the other handle “colinear and equidistant”, this behaviour needs to be configured keeping multiple handles in mind.
• [ ] Tab press while dragging an handle swaps to other handle (this should only happen if two handles are in opposite of one another and with G1 continuity enabled)
• [ ] Currently deleting an anchor adds a segment which connects the path but without the anchor point. This should not happen if the anchor is connected to more than two segments.
• [ ] If a new segment is started from an intermediate anchor (an anchor which is connected to exactly two segments), the corresponding handle at start has G1 continuity enabled, which leads to unwanted handle movements in other segments.