[DAG] Allow folding AND of anyext masked_load with >1 user to zext version

This now allows folding an AND of a anyext masked_load to a
zext_masked_load even if the masked load has multiple users.  Doing is
eliminates some redundant ANDs/MOVs for certain AArch64 SVE code.

I'm not sure if there's any cases where doing this could negatively the
other users of the masked_load.  Looking at other optimizations of
masked loads, most don't apply if the load is used more than once, so it
doesn't look like this would interfere.

Reviewed By: c-rhodes

Differential Revision: https://reviews.llvm.org/D137844