Investigate array pool usage for VBOs and TextureUploads

[peppy]

Currently we are using the ImageSharp MemoryAllocator to do all our array pool requests. It turns out that the default bucket sizes for the allocator we are using are quite small (6,16). We likely want to change to using ArrayPool directly, or adjust the sizes per use case.

Important ones are:

• ArrayPoolTextureUpload (especially on the FrameTimeDisplay which requests thousands of these - may benefit from a local pool).
• VertexBuffer, which can potentially hit the point of saturation and begin to allocate constantly.

[Flutterish]

You might be interested in how the rewrite of o!f-xr handles the array pool: MemoryPool and an example usage

[peppy]

I'm not sure how that example usage is of any relevance.

This issue can likely be closed. The first case is already refactored and the second will likely be covered by #5109.