Multiples of 4 Texture resizing flag for WinMRAssetConverter

[thmignon]

Block compression expects textures to be multiples of 4 to compress correctly. Adding a step to resize textures automatically and toggle this behavior on and off in the converter would provide a fallback when assets aren't authored with this requirement in mind.

[robertos]

I think I'll just have this on always, without a flag, on the MR converter. The compression is a required step, so I'll make sure that BC7 compressed textures are properly sized.