RFR(S): 8186716: [MVT] C2 crashes with "assert(!n->is_ValueType()) failed: value types should not be split through phis"

[Roland Westrelin]

> That's because with non-flattened value type fields (see my changes
> for 8185556), we need to "recursively" scalarize value types in
> safepoints. While processing a value type node in
> Compile::process_value_types(), other value type nodes that are on the
> _value_type_nodes list may become dead and are removed from the list
> screwing up the GrowableArray iterator. Using a node list is the
> easiest way to solve this.

Ok.

Roland.