Flymake: fix many problems with the end-of-line overlays

Flymake: fix many problems with the end-of-line overlays

bug#66041

* lisp/progmodes/flymake.el (flymake-diagnostics): Rewrite.
(flymake--really-all-overlays): Rename from flymake--overlays.
(flymake--delete-overlay): Complexify.
(flymake--highlight-line): Rework.
(flymake--handle-report): Update eol overlays
(flymake-mode): use flymake--really-all-overlays.
(flymake-after-change-function): Simplify.
(flymake-goto-next-error): Don't use flymake--overlays.