Update to SkiaSharp v3

[follesoe]

This pull request addresses #261 by upgrading the SkiaSharp dependency to v3.116.1.

The update var relatively straightforward, and the only breaking API was around the SkiaSharp.SKImageFilter.CreatePaint method call. In SkiaSharp v3 the SKImageFilter.CreatePaint method is missing and replaced with SkiaSharp.SKImageFilter.CreateShader as discussed here: mono/SkiaSharp#2569

Also, the SkiaSharp.SKImageFilter.CreateImage method does no longer take a SkiaSharp.SKFilterQuality argument, but instead a SKSamplingOptions.

If I used SKSamplingOptions.Default many of the unit tests would break. From trial and error the following SKSamplingOptions option gave most passing tests:

var sampling = new SkiaSharp.SKSamplingOptions(
                    SkiaSharp.SKFilterMode.Linear,
                    SkiaSharp.SKMipmapMode.Linear);

I still had to adjust the threshold for two tests (where manually comparing the visual results was acceptable, but the test was still failing) and skip an additional three cases (for tests that already had some skipping cases).

So far, the PR has made minimal changes to build against SkiaSharp v3. There are several build warnings due to deprecated APIs in SkiaSharp v3 that should be addressed?

Opening the PR early to get feedback and ensure this work is not a waste of time, and if @wieslawsoltes would be accepting such contributions.

Closing #261 if merged.

[wieslawsoltes]

We don't need that to be updated as current version should be backwards compatible.

[follesoe]

We don't need that to be updated as current version should be backwards compatible.

Good point @wieslawsoltes.

There are also several build warnings related to third-party dependencies such as warning NU1903: Package 'SixLabors.ImageSharp' 2.1.3 has a known high severity vulnerability.

Should we try to update these or make that a separate effort/PR?

[wieslawsoltes]

We don't need that to be updated as current version should be backwards compatible.

Good point @wieslawsoltes.

There are also several build warnings related to third-party dependencies such as warning NU1903: Package 'SixLabors.ImageSharp' 2.1.3 has a known high severity vulnerability.

Should we try to update these or make that a separate effort/PR?

I will update them later as I plan to update deps and Nuke build system to newest version.

[follesoe]

Okay, great! I'll leave the PR as is then, and will use a build of my fork until new versions are available (I am blocked on a large MAUI upgrade due to different transitive SkiaSharp dependencies)

[follesoe]

Have you had a chance to look at this @wieslawsoltes? This is blocking updates to SkiaSharp v3 and it would be great to get that updated.