intel/blorp: Handle SINT/UINT clamping on blits.

intel/blorp: Handle SINT/UINT clamping on blits.

This patch makes blorp_blit handle SINT<->UINT blit value clamping.
After reading the source's integer data (which is expanded to 32-bit),
we either IMAX with 0 (for SINT -> UINT, to clamp negative numbers) or
UMIN with (1 << 31) - 1 (for UINT -> SINT, to clamp positive numbers
outside of the representable range).

Such blits are not allowed by the OpenGL or Vulkan APIs directly:

   The Vulkan 1.1 spec for vkCmdBlitImage says:

   "Integer formats can only be converted to other integer formats with
    the same signedness."

   The GL 4.5 spec for glBlitFramebuffer says:

   "An INVALID_OPERATION error is generated if format conversions are
    not supported, which occurs under any of the following conditions:
    [...]
    * The read buffer contains unsigned integer values and any draw
      buffer does not contain unsigned integer values.
    * The read buffer contains signed integer values and any draw buffer
      does not contain signed integer values."

However, they are useful for other operations, such as texture upload
and download, which typically are implemented via blorp_blit().  i965
has code to fall back in this case (which the next commit will delete),
and Gallium expects blit() to handle this case for texture upload.

Fixes the following tests on iris:
- GTF-GL46.gtf32.GL3Tests.packed_pixels.packed_pixels
- GTF-GL46.gtf32.GL3Tests.packed_pixels.packed_pixels_pbo
- GTF-GL46.gtf32.GL3Tests.packed_pixels.packed_pixels_pixelstore

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>