Refactor call arg table updates.

Refactor call arg table updates.

When a call argument is replaced by a new node, the corresponding entry
in the call's argument table must be replaced. Managing this replacement
was a bit ad-hoc: there were a (small) number of places throughout the
compiler that needed to do so, and each determined whether or not to
call the udpate method (`fgFixupArgTabEntryPtr`) independently. The
update method has been removed and its functionality replaced with a
new method, `GenTree::ReplaceOperand`, which will update the call
argument table iff the replaced node is a call argument.

Commit migrated from https://github.com/dotnet/coreclr/commit/8ebb1d54583d0ebc03235e78e51f3026fbb7e4d3