st/mesa: improved is_interleaved_arrays() checking
st/mesa: improved is_interleaved_arrays() checking

Check that the difference in array pointers/offsets from the 0th
array are less than the stride, for both VBOs and user-space arrays.
Previously, we were only doing this for the later.

This tightens up the interleaved array test and fixes a problem with
the llvmpipe driver where we were creating way too many vertex fetch
variants only because the pipe_vertex_element::src_offset values were
changing frequently.  This change results in a 5x speed-up for one of
the viewperf tests.

Also, clean up the function to make it easier to understand.

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