Use GPUImageFilterGroup when image is center_ Inside mode is invalid to change the background color in GPUImageView

[xuzhiyong017]

What does this change?

Added the method of setting the background color, and adjust the order of the filter drawing

What is the value of this and can you measure success?

It can change the background color when gpuimageview is invalid，for example the ImageActivity

Screenshots

`

   gpuImage.setScaleType(GPUImage.ScaleType.CENTER_INSIDE)
   gpuImage.filter = GPUImageFilterGroup(listOf(GPUImageBrightnessFilter(),
        GPUImageSaturationFilter(),
        GPUImageWhiteBalanceFilter(),
        GPUImageSharpenFilter())).apply {
        setBackgroundColor(0.27f, 0.27f, 0.27f)
    }

    gpuImage.setBackgroundColor(1f,1f,1f)
    gpuImage.setImage(Uri.parse("file:///android_asset/image.png"))

`

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