* lisp/progmodes/hideshow.el: Simplify mouse binding; Use lexical-binding

* lisp/progmodes/hideshow.el: Simplify mouse binding; Use lexical-binding

(hs-set-up-overlay, hs-adjust-block-beginning): Use non-nil default for
function variables, so `add-function` can be used on them.
(hs-toggle-hiding): Make it work for mouse bindings as well.
(hs-minor-mode-map): Use it for the mouse binding.
(hs-grok-mode-type): Use bound-and-true-p.
(hs-life-goes-on): Use `declare` for the debug spec.
(hs-mouse-toggle-hiding): Make it an obsolete alias.