i965/blorp: Improve precission of blitting coordinates when clipping

i965/blorp: Improve precission of blitting coordinates when clipping

We do this in two steps: first we clip the dst rect and adjust the src
rect accordingly. Then we do it the other way around. In both passes
the adjustment part involves multiplying by a scale factor that can lead
to a small precision loss. This is breaking a few dEQP tests.

Specifically, the problem happens when we need to clip the same coordinate
twice. For example, if srcX0 and dstX0 need both to be clipped we want to
avoid the situation where we clip srcX0 first, then adjust dstX0 accordingly
but then we realize that the resulting dstX0 still needs to be clipped, so
we clip dstX0 and adjust srcX0 again. Each of these two passes can lead
to precission loss. What we want to do here is detect the rect that leads
to the largest clip (accounting for the scale factor involved), clip that
rect and adjust the other one. With this we ensure that the adjusted
coordinate does not need to be clipped again and we can skip a second pass,
improving precision.

Fixes the following 4 dEQP tests:
dEQP-GLES3.functional.fbo.blit.rect.out_of_bounds_reverse_src_x_nearest
dEQP-GLES3.functional.fbo.blit.rect.out_of_bounds_reverse_src_x_linear
dEQP-GLES3.functional.fbo.blit.rect.out_of_bounds_reverse_dst_x_nearest
dEQP-GLES3.functional.fbo.blit.rect.out_of_bounds_reverse_dst_x_linear

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Tested-by: Mark Janes <mark.a.janes@intel.com>