Use left margin to hold "=>" to indicate current error in fringeless windows

Use left margin to hold "=>" to indicate current error in fringeless windows

This applies to compilation-mode.  It amends the fix for bug #36832.

* lisp/progmodes/compile.el (compilation-arrow-overlay): renamed from
overlay-arrow-overlay.
(compilation-margin-string, compilation--dummy-string): New variables.
(compilation-set-up-arrow-spec-in-margin)
(compilation-tear-down-arrow-spec-in-margin): New functions.
(compilation-set-overlay-arrow): Rewritten to use the new variables/functions.