Frames in the debugger have right-click mouse menus, too

* sly.el (sldb-frame-menu-map): New keymap.
(sldb-frame): Use it heree.
(sldb-frame-button-near-point): First try button with
`sly-button-at' only then use `nearby-frame-button'

* lib/sly-buttons.el (sly-button-popup-part-menu): Add indirection and
fetch menu from the button.
(sly-part): Add `part-menu-keymap' prop