With this mode enabled, editing anywhere becomes possible.
All edited blocks are loaded at once when the stream is assigned.
The generator is used on the fly to fill the gaps, instead of being
pre-emptively cached only nearby the viewer to allow editing.
Editing is still on the main thread, so this can cause stalls if
the generator is complex. There is also no controlled limit on how
much data gets loaded, so if edited data is larger than RAM, it will
not be playable. The feature is already quite usable, but more work
may be done for wider viability.
