st/mesa: fix Y inversion and optimize st_BlitFramebuffer()
st/mesa: fix Y inversion and optimize st_BlitFramebuffer()

Need to check for Y inversion separately for src/dest buffers.

If both the src and dest regions are upside down, make them right-side
up for a better chance at a fast path.

progs/tests/copypixrate -blit is much faster now.

mapbox/glsl-optimizer,djreep81/glsl-optimizer,metora/MesaGLSLCompiler,mapbox/glsl-optimizer,mapbox/glsl-optimizer,tokyovigilante/glsl-optimizer,djreep81/glsl-optimizer,zeux/glsl-optimizer,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,bkaradzic/glsl-optimizer,djreep81/glsl-optimizer,jbarczak/glsl-optimizer,zz85/glsl-optimizer,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,bkaradzic/glsl-optimizer,KTXSoftware/glsl2agal,dellis1972/glsl-optimizer,adobe/glsl2agal,adobe/glsl2agal,wolf96/glsl-optimizer,mapbox/glsl-optimizer,jbarczak/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,KTXSoftware/glsl2agal,adobe/glsl2agal,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,mapbox/glsl-optimizer,metora/MesaGLSLCompiler,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,adobe/glsl2agal,benaadams/glsl-optimizer,benaadams/glsl-optimizer,benaadams/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,KTXSoftware/glsl2agal,KTXSoftware/glsl2agal,benaadams/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,zeux/glsl-optimizer,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,KTXSoftware/glsl2agal,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,adobe/glsl2agal,metora/MesaGLSLCompiler,wolf96/glsl-optimizer,benaadams/glsl-optimizer,jbarczak/glsl-optimizer