QuantizedFrame should use MemoryGroup/Buffer2D internally

[antonfirsov]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of ImageSharp
• I have verified if the problem exist in both DEBUG and RELEASE mode
• I have searched open and closed issues to ensure it has not already been reported

Description

Although it's a byte buffer, so we need an XXXXL image to make this fail, but this line is incorrect:

ImageSharp/src/ImageSharp/Processing/Processors/Quantization/QuantizedFrame{TPixel}.cs

Line 37 in b2bd68d

this.pixels = memoryAllocator.AllocateManagedByteBuffer(width * height, AllocationOptions.Clean);