Prevent overlap when `source=detect` is used

[sewnie]

When using source=detect in mode_floating, certain buttons are overlapping, making them completely unreadable and become an eye strain entirely.

There should be a check for if there are two points that are close together, the average will be used.

[moverest]

There's already a mechanism like that where it removes the inner area if its center is very close to the outer area (see src/target_detection.cpp). Feel free to try tweaking and adding new filters and see how it behaves. The approach I've taken so far has been to conservatively filter the areas. The idea is that missing an area provides a worse user experience than keeping too many — indeed, it's not possible to click on an area that doesn't exist.