implement which-key keymap based replacements

[jgrey4296]

this replaces the use of which-key-replacement-alist with the newer keymap-based-replacement approach of which-key.
It also enables evil-state based which-key bindings.

[leifhelm]

I have a configuration like this:

  (general-create-definer leader-keys
    :states '(normal insert visual emacs)
    :prefix "SPC"
    :global-prefix "C-SPC")

  (leader-keys
    "TAB" '(evil-switch-to-windows-last-buffer :which-key "Last buffer"))

It creates a message when i press SPC in normal mode:
Error running timer ‘which-key--update’: (wrong-type-argument listp "Last buffer")
And it does not display any replacements.

[leifhelm]

Suggested change

	(real-keymap (if (boundp keymap) (symbol-value keymap) (symbol-value (intern (format "%s-map" keymap)))))
	(real-keymap (general--get-keymap nil keymap nil t)))

Have a look at general--get-keymap. I found it while browsing general--define-key-dispatch