Enable Positron use

[cwickham]

Check for rstudio::readRStudioPreference() before attempting to run it.

Allows tribble_paste() to work in Positron. Positron users will get 4 spaces for a tab with no consultation of their preferences.

[MilesMcBain]

I think this was intended to be something like:

 output_context$nspc <-
  if (rstudioapi::hasFun("readRStudioPreference")) {
    rstudioapi::readRStudioPreference("num_spaces_for_tab", 4)
  } else {
    4
  }

[MilesMcBain]

I am wondering why the Positron RStudioAPI emulation does not implement studioapi::readRStudioPreference as the R VSCode extension has done?

I only say this because the function has the default argument which is already in use here to return 4 where the preference cannot be found.

So VSCode-R does:

readRStudioPreference <- function(name, default) {
    ## in future we could map some rstudio preferences to vscode settings.
    ## since the caller must provide a default this should work.
    default
}

P.S.

Thanks for taking the time to make this PR! 🙏