Implement #1008

[ilyaZar]

This PR could be used to resolve #1008 . The last bullet of the commit message is probably subject to change, also the name "class" could be altered.

The boilerplate is not minimal/empty, but one almost always uses a public interface when creating a R6 class so it may be fine if it is already there

Otherwise, works exactly the same as add_fct() and add_utils().

[ColinFay]

Hey @ilyaZar

Thanks for your work. I won't merge for now, I need to think about this a little bit but overall I think it's a great idea :)

[ilyaZar]

sure! thanks for taking time to have a look at this @ColinFay !

[VincentGuyader]

It's certain that when referring to a file, we can't use pkg and keep path. However, the meaning behind the pkg parameter isn't very clear to me. I would tend to think that it expects a character string that references a package name.

For example, this seems strange to me: pkg = get_golem_wd().

Why not use pkg_dir, or simply golem_wd when referring to the project that contains the Golem, for instance?

In any case, the deprecation of the parameter will need to be managed, with a message for users (similar to what was done in readr for transitioning from path to file).

[ilyaZar]

@VincentGuyader are you referring to #1048 ?

[ColinFay]

Will cherry pick this one in a new branch and update :) will let you know :)

[ColinFay]

Thanks, cherry picked here #1118