Fix SLDB problems after last refactoring

* sly.el (sldb-setup, sldb-insert-frames, sldb-insert-frame)
(sldb-frame-details-region): New function.
(sldb-frame-details-visible-p): Deleted.
(sldb-sugar-move,sldb-hide-frame-details, sldb-toggle-details):
Use `sldb-frame-details-region'
(sldb-sugar-move): Fix bug.
More sly-mrepl fixes

* sly-mrepl.el (sly-mrepl-mode-map): Add "M-p" and "M-n"
lost when `comint-mode-map' inheritance was broken.
(sly-mrepl--insert-output): Ensure prettier insertion of
unexpected async output.