call_standardise_formals() now attempts to standardise formals of S3 methods

[rossellhayes]

.user_code <- quote(mean(1:3))
gradethis:::call_standardise_formals(.user_code)
#> mean(x = 1:3, trim = 0, na.rm = FALSE)

^{Created on 2023-03-30 with reprex v2.0.2}