geom_rect() can derive corners from x/width or y/height

[teunbrand]

This PR aims to fix #5861.

Briefly, geom_rect() can derive the xmin/xmax/ymin/ymax parameters from x/width and y/height parameters.

The trickiest thing with this PR is what is understood as 'required aesthetics'. Currently, all the parameters mentioned above are 'optional aesthetics' and the corners ( xmin/xmax/ymin/ymax) are marked as 'non missing aesthetics'. The corners are subjected to a second check_required_aesthetics() to throw a warning.

A demo from the issue:

devtools::load_all("~/packages/ggplot2/")
#> ℹ Loading ggplot2

p <- ggplot(
  presidential,
  aes(xmin = start, xmax = end, y = forcats::fct(name))
)

p + geom_rect(height = 0.8)

However, if there is only 1 known aesthetic per position (in the example, just the y aesthetic), it'll throw an error due to missing aesthetics. It might be worth considering throwing a more tailored warning in this case.

p + geom_rect()
#> Error in `geom_rect()`:
#> ! Problem while setting up geom.
#> ℹ Error occurred in the 1st layer.
#> Caused by error in `setup_data()` at ggplot2/R/ggproto.R:190:17:
#> ! `geom_rect()` requires the following missing aesthetics: ymin and
#>   ymax.

^{Created on 2024-04-24 with reprex v2.1.0}

[teunbrand]

Possibly CI failing due to the R4.4.0 release? Will run again tomorrow.

[teunbrand]

I'm not really content with this PR as it seems like abusing the various aesthetics fields in the ggproto class. I'll put this as a draft for now.

[teunbrand]

I had to rewrite bits of check_required_aesthetics() to get around the hardcoded limit of 2 paired aesthetics, but I think this now working as it should without aesthetics field shenanigans.

[thomasp85]

LGTM