annotate() gives warning when passing position or stat

[teunbrand]

This PR aims to fix #5151.

Briefly, annotate() is hardcoded to use StatIdentity and PositionIdentity so any stat or position argument to annotate() ends up in the params to the layer. This PR warns about such cases and pre-emptively removes these arguments.

Demo:

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

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  annotate(
    "point", x = 3, y = 40,
    position = position_jitter()
  )
#> Warning: `annotate()` can't accept `position` argument.

^{Created on 2024-03-05 with reprex v2.1.0}

[thomasp85]

LGTM