intel/fs: Allow copy propagation between MOVs of mixed sizes

intel/fs: Allow copy propagation between MOVs of mixed sizes

This eliminates some spurious, size-converting moves.  For example, on
Ice Lake this helps dEQP-VK.spirv_assembly.type.vec3.i8.bitwise_xor_frag:

SIMD8 shader: 52 instructions. 1 loops. 4164 cycles. 0:0 spills:fills, 5 sends
SIMD8 shader: 49 instructions. 1 loops. 4044 cycles. 0:0 spills:fills, 5 sends

Unfortunately, this doesn't clean everything up.  Here's a subset of the
"before" assembly:

send(8)         g11<1>UW        g2<0,1,0>UD     0x02106e02
                            dp data 1 MsgDesc: ( untyped surface read, Surface = 2, SIMD8, Mask = 0xe) mlen 1 rlen 1 { align1 1Q };
mov(8)          g7<4>UB         g11<8,8,1>UD                    { align1 1Q };
mov(8)          g12<1>UB        g7<32,8,4>UB                    { align1 1Q };
send(8)         g13<1>UW        g2<0,1,0>UD     0x02106e03
                            dp data 1 MsgDesc: ( untyped surface read, Surface = 3, SIMD8, Mask = 0xe) mlen 1 rlen 1 { align1 1Q };
mov(8)          g15<1>UW        g12<8,8,1>UB                    { align1 1Q };
mov(8)          g8<4>UB         g13<8,8,1>UD                    { align1 1Q };
mov(8)          g14<1>UB        g8<32,8,4>UB                    { align1 1Q };
mov(8)          g16<1>UW        g14<8,8,1>UB                    { align1 1Q };
xor(8)          g17<1>UW        g15<8,8,1>UW    g16<8,8,1>UW    { align1 1Q };

And here's the same subset of the "after" assembly:

send(8)         g11<1>UW        g2<0,1,0>UD     0x02106e02
                            dp data 1 MsgDesc: ( untyped surface read, Surface = 2, SIMD8, Mask = 0xe) mlen 1 rlen 1 { align1 1Q };
mov(8)          g7<4>UB         g11<8,8,1>UD                    { align1 1Q };
send(8)         g13<1>UW        g2<0,1,0>UD     0x02106e03
                            dp data 1 MsgDesc: ( untyped surface read, Surface = 3, SIMD8, Mask = 0xe) mlen 1 rlen 1 { align1 1Q };
mov(8)          g15<1>UW        g7<32,8,4>UB                    { align1 1Q };
mov(8)          g8<4>UB         g13<8,8,1>UD                    { align1 1Q };
mov(8)          g16<1>UW        g8<32,8,4>UB                    { align1 1Q };
xor(8)          g17<1>UW        g15<8,8,1>UW    g16<8,8,1>UW    { align1 1Q };

There are a lot of regioning and type restrictions in
fs_visitor::try_copy_propagate, and I'm a little nervious about messing
with them too much.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Suggested-by: Francisco Jerez <currojerez@riseup.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9025>