One last compile test then seek agreement to cherrypick https://www.sqlite.org/cgi/src/artifact/c16c855f7e2ef5bf into trunk.

This represents a lot of research into what the functions do and how they relate to each other, vedbe and pager.

There are a couple of other minor comment changes, however, there is also an accidental import of trunk updates through a Fossil error. So that is why cherrypicking is needed.https://www.sqlite.org/cgi/src/artifact/c16c855f7e2ef5bf