For cases in which the requirements of the GPU API prevent directly
uploading a texture with a given stride, we need to fix the stride
manually in host memory. This incurs an extra memcpy, but there's not
much we can do about it. (Even in `ra_gl` land, the driver will just
hide this memcpy from the user)
Note: This code could be done better. It could only copy as many texels
as needed, and it could pick a stride that's a multiple of
`gpu->limits.align_tex_xfer_stride` for better performance. Patches
welcome (tm)
Fixes#7759
Niklas Haas
b16d8865b7