Expand the inline help text displayed for theme_sub_*() functions.

[ujtwr]

The introduction of theme_sub_*() functions has made it much easier to structure and organize theme() customizations. However, when coding in RStudio, the inline help text shown for these functions is always the generic message:

"Arguments that are renamed and passed on to theme()."

As a result, users must manually consult the documentation for theme() to understand the meaning of the available arguments.

Since RStudio already displays inline help during code completion, it would be much more useful if the corresponding documentation from theme() were shown directly for each argument. This would reduce the need to switch between code and documentation and could significantly improve coding efficiency when working with ggplot2 themes.

[teunbrand]

All the theme_sub_*() family members currently share the documentation, so there isn't a readily available opportunity to document these individually. The pain point is that theme_sub_axis(ticks) and theme_sub_legend(ticks) share the argument name, but have disparate interpretations. Even if we create the opportunity by splitting up the documentation, it would be an large duplication to carry over all information from theme(). The loss of a single source of truth for this documentation makes maintenance more inconvenient. I like that theme()'s docs are currently the authoritative documentation on the subject, so I'm reluctant to change this for the convenience of inline help.

[ujtwr]

In practice, this is not a major issue because I am already familiar with most theme() options. However, there are occasional situations where I want to quickly confirm the meaning of a particular argument, and having that information available inline would be convenient.

One reason I find this useful is that the documentation for theme() contains a very large number of options, making it somewhat cumbersome to search for the relevant entry each time. Displaying the corresponding argument descriptions directly in the inline help for theme_sub_*() functions would make those occasional lookups much faster.

That said, I also understand that there may be maintenance and documentation-generation challenges associated with keeping such information synchronized. Therefore, I am not proposing this as a high-priority issue, but rather as a potential usability enhancement. If an opportunity arises in the future, I would appreciate it if this suggestion could be kept in mind.