Update Command Loop chapter of Lisp manual.

Update Command Loop chapter of Lisp manual.

* doc/emacs/commands.texi (Command Overview): Mention read-key.
(Using Interactive, Interactive Call): Minor clarifications.
(Function Keys, Click Events): Avoid "input stream" terminology.
(Click Events): Add xref to Window Sizes and Accessing Mouse.
Clarify column and row components.
(Accessing Mouse): Add xref to Click Events.  Minor fixes.
(Special Events): Copyedits.

* doc/emacs/streams.texi (Input Streams): De-document get-file-char.
(Output Variables): Don't refer to old backquote syntax.