Modules are now first-class objects in the VM. This allows us to remove
the top-level object, clean up core::bootstrap, and remove
core::globals (in favour of using core::bootstrap directly). As part of
this we also remove Trait.implement(), instead implementing traits using
compiler generated code. Trait.implement() could not be safely used
anyway, as it only copied over default methods; without verifying if all
required methods are implemented.

All of this makes it easier to implement the self-hosting compiler: the
top-level object no longer needs to be supported, and we can treat
core::bootstrap like any other module. This in turn allows us to use a
more efficient way of storing type information in various places.