Support a new ["..."] key binding syntax

* doc/lispref/keymaps.texi (Key Sequences):
(Changing Key Bindings): Document the various key syntaxes.

* lisp/emacs-lisp/byte-opt.el (byte-optimize-define-key)
(byte-optimize-define-keymap)
(byte-optimize-define-keymap--define): New functions to check and
expand ["..."] syntax at compile time.

* src/keymap.c (Fdefine_key): Understand the ["..."] syntax.
(syms_of_keymap): Define `kbd' symbols.

lisp/emacs-lisp/byte-opt.el

@@ -1186,6 +1186,67 @@ See Info node `(elisp) Integer Basics'."
 
 (put 'concat 'byte-optimizer #'byte-optimize-concat)
 
+(defun byte-optimize-define-key (form)
+  "Expand key bindings in FORM."
+  (let ((key (nth 2 form)))
+    (if (and (vectorp key)
+             (= (length key) 1)
+             (stringp (aref key 0)))
+        ;; We have key on the form ["C-c C-c"].
+        (if (not (kbd-valid-p (aref key 0)))
+            (error "Invalid `kbd' syntax: %S" key)
+          (list (nth 0 form) (nth 1 form)
+                (kbd (aref key 0)) (nth 4 form)))
+      ;; No improvement.
+      form)))
+
+(put 'define-key 'byte-optimizer #'byte-optimize-define-key)
+
+(defun byte-optimize-define-keymap (form)
+  "Expand key bindings in FORM."
+  (let ((result nil)
+        (orig-form form)
+        improved)
+    (push (pop form) result)
+    (while (and form
+                (keywordp (car form))
+                (not (eq (car form) :menu)))
+      (push (pop form) result)
+      (when (null form)
+        (error "Uneven number of keywords in %S" form))
+      (push (pop form) result))
+    ;; Bindings.
+    (while form
+      (let ((key (pop form)))
+        (if (and (vectorp key)
+                 (= (length key) 1)
+                 (stringp (aref key 0)))
+            (progn
+              (unless (kbd-valid-p (aref key 0))
+                (error "Invalid `kbd' syntax: %S" key))
+              (push (kbd (aref key 0)) result)
+              (setq improved t))
+          ;; No improvement.
+          (push key result)))
+      (when (null form)
+        (error "Uneven number of key bindings in %S" form))
+      (push (pop form) result))
+    (if improved
+        (nreverse result)
+      orig-form)))
+
+(defun byte-optimize-define-keymap--define (form)
+  "Expand key bindings in FORM."
+  (let ((optimized (byte-optimize-define-keymap (nth 1 form))))
+    (if (eq optimized (nth 1 form))
+        ;; No improvement.
+        form
+      (list (car form) optimized))))
+
+(put 'define-keymap 'byte-optimizer #'byte-optimize-define-keymap)
+(put 'define-keymap--define 'byte-optimizer
+     #'byte-optimize-define-keymap--define)
+
 ;; I'm not convinced that this is necessary.  Doesn't the optimizer loop
 ;; take care of this? - Jamie
 ;; I think this may some times be necessary to reduce ie (quote 5) to 5,