[InstCombine] Properly combine metadata when replacing a load with another

[InstCombine] Properly combine metadata when replacing a load with another

Not doing this can lead to misoptimizations down the line, e.g. because
of range metadata on the replacing load excluding values that are valid
for the load that is being replaced.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241886 91177308-0d34-0410-b5e6-96231b3b80d8