sdBox version of [RadialGradient]
This is an implemetation of the signed distance field "Box - Exact" desbribed  in the "2D distance functions" article on Inigo Quilez's website.

sdBox function is replaced by sdRoundedBox

plus presets

# Conflicts:
#	.Variations/dc2273a7-8a54-4e6f-8d8e-9a675c1ef599.var
#	Operators/Types/lib/img/generate/BoxGradient.cs
#	Operators/Types/lib/img/generate/BoxGradient_dc2273a7-8a54-4e6f-8d8e-9a675c1ef599.t3
#	Operators/Types/lib/img/generate/BoxGradient_dc2273a7-8a54-4e6f-8d8e-9a675c1ef599.t3ui
#	Operators/Types/lib/img/generate/NGonGradient.cs
#	Operators/Types/lib/img/generate/NGonGradient_05463270-37d4-400f-8d0d-c50f81663304.t3
#	Operators/Types/lib/img/generate/NGonGradient_05463270-37d4-400f-8d0d-c50f81663304.t3ui

…ut field background color

This allows to reduce the size of region where at point lighth as max intensity. Previously without this option, increasing the decay rate would not reduce the radius of that region below roughly 0.6 distance units).

float intensity = Lights[i].intensity / (pow(distance / Lights[i].range, Lights[i].decay) + 1);

…on ops like [ParticleSystem] when rendering videos with low fps

…oming in mini map

# Conflicts:
#	Operators/Types/lib/anim/Accumulator.cs

…xt state)

Make OutputMergerStage operator restore state properly (and avoir an hidden alloc)
Cache windows to draw in Window to avoid creating and array every frame