Rename trans arguments to transform

[teunbrand]

This PR aims to fix #5558.

Briefly, we follow in {scales}'s footsteps by renaming the trans argument to transform.
This mostly affects scale functions and the secondary axis functionality.

[teunbrand]

This is the crux of the PR. If trans is used, we assume they meant transform instead.

[teunbrand]

Yes good call, thanks for catching that!

[teunbrand]

I'm still somewhat worried that renaming the trans ggproto field will have a non-trivial impact on scale extensions.
Not all scale extensions run through the continuous/binned/discrete_scale() constructors that would populate the transformer field. An example what I could see going wrong in extensions are cases such as this:

https://github.com/tidyverts/tsibble/blob/04b36e7ee9ed4c7bded6b4b938275a0f23da6bd0/R/scales.R#L52-L60

[thomasp85]

yeah, that was kind of the cases we were worried about - let's keep the field name as is

[thomasp85]

or, we could do both an do a soft-deprecation inside the transform() method where it checks whether trans is NULL

[thomasp85]

Just to be sure, have you tested this branch against a scale extension that uses trans?

[teunbrand]

Yeah I tested it against an extension and trans gets funneled to transformation when used with a proper constructor. I don't think the {tsibble} example I linked to earlier works as it should. Because scale_x_date() is used to construct the ggproto object that is inherited from, the transformation field is populated and transformation %||% trans thus returns the transformation field.

[teunbrand]

Should now be better backwards compatible:

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

ggplot(economics[1:20,], aes(date, unemploy)) +
  geom_line() +
  tsibble::scale_x_yearquarter()
#> Warning: Scale$trans was deprecated in ggplot2 3.5.0.
#> ℹ Please use Scale$transformation instead.
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.

^{Created on 2023-12-14 with reprex v2.0.2}

[thomasp85]

LGTM

[teunbrand]

Thanks for the review Thomas!