RFR(M): 8211772: [lworld] Support for non-scalarized value types

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8211772
http://cr.openjdk.java.net/~thartmann/8211772/webrev.00/

To be able to support nullable value types in C2, we need support for disabling scalarization and
pass values as oops. This patch adds a debug flag -XX:ScalarizeValueTypes that disables
scalarization for all value types. We can remove the checks for constant null as soon as we get
additional guarantees from the verifier.

This change also contains a lot of refactoring of (partially) unrelated code.

The next step will be to implement nullable value types on top of this.

Thanks,
Tobias