Enable any preference to be project-specific

[jmcphers]

Currently, only a small handful of RStudio preferences can be set on a project (not global) level. These preferences are written inside the.Rproj file.

As part of the user preference overhaul in RStudio in #5069, we introduced all of the architecture required to support project-level control over any preference. However, this was not connected, because:

• we had no UI gesture that could be used to set a preference for a particular project instead of globally, and
• we had no storage for arbitrary project-level prefs (except the aforementioned .Rproj)

Both of these are still a problem; this issue tracks the work needed to make any preference settable at the project level. This would resolve a long tail of requests for project-specific settings; for example:

#7130 - Spellcheck language
#4335 - Margin column
#2350 - Theme
#9409 - Pipe operator
etc., etc.

[salim-b]

Source column layout, too, please! 🙃

[aja08379]

Per project R versions have also been requested (Pro customer)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs, per https://github.com/rstudio/rstudio/wiki/Issue-Grooming. Thank you for your contributions.

[GegznaV]

What are the plans (timeline) for implementing this feature?