hideshow.el: Improve hs-toggle-hiding behavior

hideshow.el: Improve hs-toggle-hiding behavior

* lisp/progmodes/hideshow.el
(hs-find-block-beginning-match): New function to be used in
`hs-already-hidden-p'.
(hs-already-hidden-p): Add check if beginning of line is inside a
block.
(hs-toggle-hiding): Don't change to selected-window's buffer when
event arg is absent.

* test/lisp/progmodes/hideshow-tests.el
(hideshow-tests-with-temp-buffer-selected): New helper macro.
(hideshow-tests-make-event-at): New helper function.
(hideshow-already-hidden-p-1): New test.
(hideshow-toggle-hiding-1): New test.
(hideshow-mouse-toggle-hiding-1): New test (bug#52092).