Scale contraints for 2D facets

[teunbrand]

Consider the following plot where x/y are free.

SELECT bill_len, bill_dep, species, island FROM ggsql:penguins
VISUALISE bill_len AS x, bill_dep AS y
DRAW point
FACET species BY island SETTING free => ['x', 'y']
LABEL
  title => 'Bill Dimensions by Species and Island',
  x => 'Bill Length (mm)',
  y => 'Bill Depth (mm)'

There are a few things wrong with this plot:

• BUG: The data-to-panel mapping is wrong.
  • Adelie penguins live on all three islands.
  • Chinstrap only on dream
  • Gentoo only on Biscoe.
• BUG: Position scales are anchored to 0 for no apparent reason.
• ENHANCEMENT: Position scales are free per-panel. In ggplot2, we have free scales per row/column. We should at least allow for ggplot2's behaviour of fixing x scales within a column and fixing y scales within a row to be an option.