RFR(XS): 8228367: [lworld] Constant, null-free inline type fields should be treated as flattenable

[Tobias Hartmann]

Hi,

please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8228367
http://cr.openjdk.java.net/~thartmann/8228367/webrev.00/

When loading a constant, null-free inline type field from an inline type, we should treat that field
as flattenable (even if it is not declared as flattenable) to trigger scalarization.

I also had to remove the assert in ValueTypeNode::pass_fields because it is too strong.

Thanks,
Tobias