Resolvesgodotengine/godot-proposals#1246.
It is difficult to tell the difference between the handles for adjusting
curves and the points themselves when looking at a Path gizmo.
This re-uses the icons used for Path2D.
Unlike Path2D, this does not use a different icon for smooth vs sharp
points, as using a potentially different material for each point would
prevent batching the points in add_handles (and adding them out-of-order
messes up other logic based on handle indices).
This includes a public API change to allow specifying a texture for a
handle material. This allows spatial gizmo plugins to customize the way
a handle is rendered, if desired, but does not break existing behavior
(as providing no texture uses the default).
The path handle icons were resized as well. 16x16 is the standard icon
size. These icons were 10x10 rather than 16x16, and appeared rather
small in the editor.
To resize, I:
- Opened the original in Inkscape
- Resized the document to 16x16
- Opened the transform dialog
- Scaled by 160% proportionally
- Used Align/Distribute to center on the page
- Saved the document
- Cleaned with `svgcleaner --multipass`
