[Inline] Fix incorrect noalias metadata application (PR48209)

The VMap also contains a mapping from Argument => Instruction,
where the instruction is part of the original function, not the
inlined one. The code was assuming that all the instructions in
the VMap were inlined.

This was a pre-existing problem for the loop access metadata, but
was extended to the more common noalias metadata by
27f647d1, thus causing miscompiles.

There is a similar assumption inside CloneAliasScopeMetadata(), so
that one likely needs to be fixed as well.