Fix string reverse member overload name

[TristonianJones]

Update the string reverse() overload id to be unique to the type.

In the future overload IDs for a given function should not be equal to
the function name as this can interfere with dynamic dispatch for a
parsed-only expression.

This change should be a no-op for anyone using reverse today as
the behavior will effectively cause existing expressions to use the
dynamic dispatch rather than the specific overload once more overloads
are introduced under the reverse function.