These infallible resource factory functions were only there to ease the
conversion to the new factory functions. Since all child classes of
VMObject now use the fallible resource factory functions, we don't
need the infallible versions anymore.
This commit moves the allocation of the resources required for VMObject
from its constructors to the constructors of its child classes.
We're making this change to give the child classes the chance to expose
the fallibility of the allocation.
FixedArray now doesn't expose any infallible constructors anymore.
Rather, it exposes fallible methods. Therefore, it can be used for
OOM-safe code.
This commit also converts the rest of the system to use the new API.
However, as an example, VMObject can't take advantage of this yet,
as we would have to endow VMObject with a fallible static
construction method, which would require a very fundamental change
to VMObject's whole inheritance hierarchy.
The VMObject class now manages its own instance list (it was previously
a member of MemoryManager.) Removal from the list is done safely on the
last unref(), closing a race window in the previous implementation.
Note that VMObject::all_instances() now has its own lock instead of
using the global MM lock.
