SparkR 2.3 QA: Programming guide, migration guide, vignettes updates

Before the release, we need to update the SparkR Programming Guide, its migration guide, and the R vignettes. Updates will include:

• Add migration guide subsection.
  • Use the results of the QA audit JIRAs.
• Check phrasing, especially in main sections (for outdated items such as "In this release, ...")
• Update R vignettes

Note: This task is for large changes to the guides. New features are handled in SPARK-23116.