New window change functions in Emacs 27

[Alexander-Miller]

Something to remember later:

Window change functions have been redesigned completely.
Hooks reacting to window changes run now only when redisplay detects
that a change has actually occurred. The four hooks provided are:
'window-buffer-change-functions' (run after window buffers have
changed), 'window-size-change-functions' (run after a window was
assigned a new buffer or size), 'window-configuration-change-hook'
(like the former but run also when a window was deleted) and
'window-selection-change-functions' (run when the selected window
changed). 'window-scroll-functions' are unaffected by these changes.

[Alexander-Miller]

window-configuration-change-hook is still valid and the new functions are not needed outside of #328, so there is nothing to do here.