* Move initial batch of shaders and presets to smoothing subdirectory
* Rename smoothing to edge enhancement
* Move cubic and windowed into interpolation
* Fix some presets
* Fix rest of presets
* Rename edge-enhancement to edge-smoothing
* Move pixel art scalers into separate directory separate from 'interpolation'
* Flatten interpolation/cubic into interpolation/
* Simplify pixel AA; Dependents to be refactored
* Finish refactoring pixel_aa itself; Dependent presets TBD
* Update average and border fill
* Tune default blur strengths in blur fill
* Clean up includes
* Minor corrections
Features:
- produces nearest neighbor look with fractional scales.
- uses texture AA shader code.
- uses hotizontal subpixel scaling.
- due to different pixel sizes, moving sprites change dimension if nearest neighbor is used with fractional scaling. This looks unsteady. This shader uniforms pixel dimensions. Output looks much quieter.
https://forums.libretro.com/t/uniform-nearest-interpolation-shader/41492
