enhance: type ``` and press Enter to switch to codemirror

src/main/frontend/state.cljs

@@ -688,7 +688,6 @@
 
 (defn drop-last-selection-block!
   []
-  (def blocks (:selection/blocks @state))
   (let [last-block (peek (vec (:selection/blocks @state)))]
     (swap! state assoc
            :selection/mode true
@@ -874,6 +873,12 @@
                       :editor/block nil
                       :cursor-range nil}))
 
+(defn into-code-editor-mode!
+  []
+  (swap! state merge {:editor/editing? nil
+                      :cursor-range nil
+                      :editor/code-mode? true}))
+
 (defn set-last-pos!
   [new-pos]
   (set-state! :editor/last-saved-cursor new-pos))