* Laid groundwork for per-stroke brush parameters.
* Added new spacing parameter.
* Added back interpolation, using spacing parameter.
* Move bounding box code into core.
* Initial working prototype of per-stroke styles.
* Removed now useless brush node properties.
* Made default spacing 50% for performance comparison.
* Quick and dirty prototype for BlitNode copied from blend.
* Fixed error after rebase.
* Optimized the blitting loop.
* Pretty big optimization for into_flat_u8.
* Insert brush node for images
* Fix starting position transform
* UX polish
* Code review nits
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Co-authored-by: 0hypercube <0hypercube@gmail.com>
Co-authored-by: Keavon Chambers <keavon@keavon.com>