[enhancement]: Duplicate and Complement regions

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Contact Details

clsn on discord

### What should this feature add?

Regarding regional prompting and auto-negative.
Sometimes, auto-negative isn't what you really want. You'd like to be able to say "I want _this_ negative prompt in the complement of _that_ region." If I have a region that contains "an adorable long-haired cat," I'd like the complement of that region to have "cat" as its negative prompt, but not necessarily the qualifiers.
Also, at least in a video presentation someone wound up drawing two regions that were more or less the same. So probably the simplest and most flexible way to do this is to have a "duplicate this region/layer" action, and a "take the complement of this region" switch or button, so the user can compose these things as needed. That seems like the most intuitive and flexible way to provide this.

### Alternatives

Other possibilities are more complicated, "linking" a layer to its complement (which has the advantage that editing the region automatically updates the complement, but I don't think that's really an important advantage). The "take the complement of this layer" could be a switch (setting a flag or something) or it could be an operation (actually converting the region); either way would be okay and would probably be about the same for the user.

### Additional Content

_No response_