Fix SBCG in value-numbering constant assertprop

Fix SBCG in value-numbering constant assertprop

Value-numbering can assign the same value number to nodes
of different type as long as they have the same bit-representation.
However when substituting a constant into a tree node of different
type, we want the bit-exact representation and not the same value.
Assertion prop should reinterpret int/float value changes rather
than coercing them.

Add an il test that exposes a bug in assertionprop when doing
value-numbering based constant propagation. A cpblk can be used
to copy a scalar value between differing types but for which there
is no change in bit representation.

Commit migrated from https://github.com/dotnet/coreclr/commit/9a6a40d9edcc3ea85a005afc3727d4fc0cc2ae7c