Exclude labels from aes_params field

[teunbrand]

This PR aims to fix #6003.

Briefly, any aesthetic in layer$computed_mapping that has an equivalent in layer$aes_params is excluded from contributing to the labels. Reprex from issue, please note the label at the colourbar is G and not <<< G >>> or g from the 1st layer.

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

d <- data.frame(x = 1, y = 2, g = 3)
d2 <- d
colnames(d2) <- c("X", "Y", "G")

attr(d[[1L]], "label") <- "<<< X >>>"
attr(d[[2L]], "label") <- "<<< Y >>>"
attr(d[[3L]], "label") <- "<<< G >>>"

ggplot() +
  geom_point(data = d, aes(x, y, colour = g), colour = "grey") + 
  geom_point(data = d2, aes(X, Y, colour = G))

^{Created on 2024-07-17 with reprex v2.1.1}

[yutannihilation]

Looks good! Thanks for fixing so quickly.

[teunbrand]

Thanks for the review!