Density component

[olliethomas]

[OPTIONAL] Is your feature request related to a problem? If so, please describe.
There's been a couple of times where we are extracting information from the tool and calculating observations per area in a spreadsheet. This feels like the sort of thing that could be a model component.

Describe the feature you'd like
Maybe input of a mask, and another or observations, and there is no output as such, but a chart is produced, like the bar chart component.

Describe alternatives you've considered
We can do this in a spreadsheet. We can continue to do this, but it seems like the sort of thing we might do fairly regularly.

Additional context
See ladybirds and multiple value of trees conversation.