Make Brush tool use per-stroke options and improve its performance (#1242)

* 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>

node-graph/gcore/src/raster.rs

@@ -8,6 +8,7 @@ use glam::DVec2;
 pub use self::color::{Color, Luma};
 
 pub mod adjustments;
+pub mod bbox;
 #[cfg(not(target_arch = "spirv"))]
 pub mod brightness_contrast;
 pub mod color;