Capture error with hint when piping plots into facets

[mitchelloharawild]

Resolves #4379

Piping a plot into a layer() gives a helpful error with a hint:

ggplot(diamonds) %>% 
  geom_point(aes(price, carat))
#> Error: `mapping` must be created by `aes()`
#> Did you use %>% instead of +?

This pull request adds this hint and better captures the error when piping into facets:

Before

library(ggplot2)
library(magrittr)
ggplot(diamonds) %>% 
  facet_grid(vars(cut))
#> Error: `rows` must be `NULL` or a `vars()` list if `cols` is a `vars()` list
ggplot(diamonds) %>% 
  facet_grid()
#> <ggproto object: Class FacetGrid, Facet, gg>
#>     compute_layout: function
#>     draw_back: function
#>     draw_front: function
#>     draw_labels: function
#>     draw_panels: function
#>     finish_data: function
#>     init_scales: function
#>     map_data: function
#>     params: list
#>     setup_data: function
#>     setup_params: function
#>     shrink: TRUE
#>     train_scales: function
#>     vars: function
#>     super:  <ggproto object: Class FacetGrid, Facet, gg>
ggplot(diamonds) %>% 
  facet_wrap(vars(cut))
#> Warning: Coercing `nrow` to be an integer.
#> Error in sanitise_dim(nrow): 'list' object cannot be coerced to type 'integer'
ggplot(diamonds) %>% 
  facet_wrap()
#> <ggproto object: Class FacetWrap, Facet, gg>
#>     compute_layout: function
#>     draw_back: function
#>     draw_front: function
#>     draw_labels: function
#>     draw_panels: function
#>     finish_data: function
#>     init_scales: function
#>     map_data: function
#>     params: list
#>     setup_data: function
#>     setup_params: function
#>     shrink: TRUE
#>     train_scales: function
#>     vars: function
#>     super:  <ggproto object: Class FacetWrap, Facet, gg>

^{Created on 2021-03-23 by the reprex package (v1.0.0)}

After

library(ggplot2)
library(magrittr)
ggplot(diamonds) %>% 
  facet_grid(vars(cut))
#> Error: `rows` must be `NULL` or a `vars()` list if `cols` is a `vars()` list
#> Did you use %>% instead of +?
ggplot(diamonds) %>% 
  facet_grid()
#> Error: Please use `vars()` to supply facet variables
#> Did you use %>% instead of +?
ggplot(diamonds) %>% 
  facet_wrap(vars(cut))
#> Error: Please use `vars()` to supply facet variables
#> Did you use %>% instead of +?
ggplot(diamonds) %>% 
  facet_wrap()
#> Error: Please use `vars()` to supply facet variables
#> Did you use %>% instead of +?

^{Created on 2021-03-23 by the reprex package (v1.0.0)}

[yutannihilation]

Looks perfect, thanks!