IRListView is now purely a view type. Instead, ownership is managed on-demand
by a separate interface (IRStorageBase). Materialization of IRListViews to
owning types is moved to this interface as well.
This also avoids unneeded copies of the data.
This is no longer necessary to be part of the public API. Moves the
header internally.
Needed to pass through `IsAddressInCodeBuffer` from CPUBackend through
the Context object, but otherwise no functional change.
Tony Wasserka