Generalize "RStudio" messages/documentation #2182
Description
Lots of places (particularly in R/r.R triggered this ticket but I know there are a bunch in R/edit.R and also probably others) mention "RStudio" where "RStudio or Positron" (or "Positron or RStudio") would be more appropriate, or possibly "your IDE" to generalize in case eventually it works in vscode or something. The specific trigger was the "No file is open in RStudio." error in compute_active_name in r.R, but there are also a lot of mentions in documentation.
Some mentions seem like they are probably still RStudio-specific (like everything in R/addin.R and R/rstudio.R, and the new stuff in R/air.R), so updating these will take some care.