Expose ability to create and render textures from arbitrary RGBA buffers

[kunitoki]

I need to be able to render images using the rive renderer but the method:

    virtual rcp<Texture> makeImageTexture(uint32_t width,
                                          uint32_t height,
                                          uint32_t mipLevelCount,
                                          const uint8_t imageDataRGBA[]) = 0;

is protected inside the RenderContextHelperImpl class, making it impossible to reach from a consumer of the rendering api. I already do the image decoding myself and it would be overkill to do it twice using the Factory decodeImage, we would need a new Factory::makeImageTexture for that to work. The same might apply to the fonts, so we are missing Factory::makeFont allowing to pass an arbitrary byte buffer.

Moreover, the class RiveRenderPath is a private implementation detail but it seems it is the only way to achieve image rendering directly, so i cannot compile this code without exposing the class to the headers.

    rive::RiveRenderPaint paint;
    paint.image (image.getTexture(), jlimit (0.0f, 1.0f, options.opacity));
    paint.blendMode (toBlendMode (options.blendMode));
    renderer.drawPath (unitRectPath.get(), &paint);

Any feedback if this could be opened up in the api ?