Savestate/bk2 `Framebuffer` isn't easily user-accessible

[Morilli]

Ever since the zstd compression changes, the Framebuffer*.bmp files are zstd-compressed, which makes them unviewable unless they are manually extracted and decompressed with zstd beforehand.

There is another, technically unrelated problem where the Framebuffer.bmp in a .bk2 isn't actually in .bmp format, it's just the raw framebuffer. However the Branches/FrameBuffer*.bmp of a .tasproj are in bmp format, as well as the FrameBuffer.bmp file saved in a .State file.

So I wanna propose two changes (that would require bumping the BizState version):

1. Make the Framebufer.bmp always contain valid bmp data as the file extension suggests instead of just saving the raw frame buffer in the case of a .bk2 movie.
2. Don't zstd-compress .bmp files or at the very least not the main one inside of a .bk2 or .State file, as it prevents users from viewing them normally and based on some short testing, the difference in compression strength and speed is negligible between zstd and zip.