[FEATURE] Expose API for registering new codecs

[TomEdwardsEnscape]

Is your feature request related to a problem?

I want to add new image codecs for image formats which are not supported by the built-in Skia codecs. This is not currently possible, even though Skia itself supports it. There is no C# API and the C++ API has been excluded from the native library.

Describe the solution you would like

The native API, SkCodec::Register, requires a pointer to a C++ object.

Since this is not easy to wrap in C#, it would be acceptable just to expose the native API in your build of the native Skia library. We can then write and register a codec ourselves in a small native library.

• Method Declaration
• Method Definition

Describe alternatives you have considered

There are no alternatives.

Additional context

No response

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