Layer and grid snapping systems

[0HyperCube]

Closes #1206 closes #318 closes #633

Functionality

• Free snapping
• Contrained snapping (e.g. drag on one axis with select, or constrained aspect ratio with rectangle tool)

Tools

• Select
• Path
• Pen
• Line
• Rect
• Circle
• Shape

Bounds snapping

• edges
• corners
• edge midpoints
• centres
• overlays

Node snapping

• paths
• path_intersections
• cusp_nodes
• smooth_nodes
• line midpoints
• normals
• tangents
• overlays

Grid snapping

• to line
• to intersections
• overlays
• Customise offset and size
• isometric grid

[otdavies]

Amazing work, really excited to see the isometric especially.

Note: Going to zero or negative spacing seems to cause an editor freeze.

[otdavies]

Another note:

Looks like in certain situations while scaling there is a jumpy / jittery behavior while snapping..
Example:
https://github.com/GraphiteEditor/Graphite/assets/3145170/31f2cb9b-102d-4212-9797-8e1d7ece408a

File (remove the .json): example.graphite.json

[0HyperCube]

Note: Going to zero or negative spacing seems to cause an editor freeze.

Fixed @otdavies

Looks like in certain situations while scaling there is a jumpy / jittery behavior while snapping..

This was caused by a NaN being produced when calculating the X distance. I added a check to avoid this and fix the behaviour.

[Keavon]

Freakin' amazing!