Introduce new value t for compilation-context-lines to eliminate scrolling

Introduce new value t for compilation-context-lines to eliminate scrolling

In particular, to prevent scrolling in a window lacking a left fringe.
Instead, a visible arrow "=>" is inserted before column zero.  This fixes
bug #36832.

* lisp/progmodes/compile.el (compilation-context-lines): Add the new value t.
(compilation-set-window): Amend to handle compilation-context-lines being t.
(overlay-arrow-overlay): New variable holding an overlay with before-string
property "=>".
(compilation-set-overlay-arrow): New function which manipulates
overlay-arrow-overlay.
(compilation-goto-locus, compilation-find-file): In addition to calling
compilation-set-window, also call compilation-set-overlay-arrow.

* doc/emacs/building.texi (Compilation Mode): Document the new value t which
compilation-context-lines can take.

* etc/NEWS: Add an entry for this change.