Disconnect {Lithium,NeonSR2} implementations

We will need to define two new serialization formats: one
sharing object value serialization (for NeonSR3) and one
disconnected from it (for Magnesium).

In order to maintain scalability with so many formats, we want
to avoid JIT considering implementations which were not referenced
at runtime. This should make CHA and method dispatch more
efficient.

Since we are isolating things, we also pull ValueTypes lookups
and keep it in the same class for easier understanding.

Change-Id: I3db4e9633db4a75016e17ac31bb38452bcb9f42a
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>