bug#67382: 26.3; Emacs manual: clarify notions/names "visual line" and "screen line"

[Drew Adams <drew.adams@oracle.com>]

Close if you don't think this is a bug.  But in that case please point
to / explain where this is explained/defined in the manual.

There are multiple functions/commands that have `visual' in their name,
and refer to "visual lines".  And there is `visual-line-mode', which is
not necessarily involved/required for such functions.

I haven't found a definition of "visual line" in the manual.  But I do
see a definition of "screen line", in node `Continuation Lines'.  Is
"visual line" synonymous with "screen line"?  If so, should "visual line"
replace "screen line", since there are line-oriented functions with
`visual' in their name?

Please take a look, and if relevant fix the manual to make this clear.
Functions whose doc strings or manual doc refers to "visual line" should
be able to be understood by referring to some definition/explanation of
"visual line" in the manual.  The only index entry matching "visual
line" is for node `Visual Line Mode'.  The Glossary refers only to
"screen lines", not "visual lines" - there's no match for "visual" in
the Glossary at all.

In GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
 of 2019-08-29
Repository revision: 96dd0196c28bc36779584e47fffcca433c9309cd
Windowing system distributor `Microsoft Corp.', version 10.0.19045
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static -g3''