Add new paint: conical gradient

[tinchodias]

Similar to linear and radial gradient.

Extracted from #191

[tinchodias]

Take into account: AthensSurfaceExamples class>>#exampleConicalGradient which references to https://blogs.igalia.com/dpino/2020/06/11/renderization-of-conic-gradients/

[tinchodias]

An implementation: https://gitlab.freedesktop.org/cairo/cairo/-/blob/master/test/mesh-pattern-conical.c

[tinchodias]

Candidate name: BlConicalGradientPaint

[LabordePierre]

Thanks @tinchodias to add it :) A typical use case is:

[tinchodias]

Note: It is called "conical" in Krita, but there are 2 variants: conical and conical-symmetric
https://docs.krita.org/en/reference_manual/tools/gradient_draw.html

@labordep do you think "conical" is the right name, or you vote for "angular"?

[LabordePierre]

I don't know, conical is good because this the shape from a top point of view!

[tinchodias]

This Alexandrie example deserves to be mentioned here: AeCairoMigratedRenderTest>>#surfaceWithMeshPatternConical