Issue #5411: Import DDS BC7 compression
This is a draft merge request to resolve issue #5411 (closed).
It adds support for loading DDS files with BC7 compression. The implementation is based off ImageMagick's. Documentation for the format can be found at https://learn.microsoft.com/en-us/windows/win32/direct3d11/bc7-format.
@Stayd had previously mentioned working on this a year ago - if they're still interested, I'm happy to close this MR so they can post their own work.