[FIXED JENKINS-23151, JENKINS-23026] Save CodeMirror editor when it loses focus

* Save CM editor when it loses focus to ensure that test is saved back to textarea
* Turn on again CM editor for shell scripts

core/src/main/resources/hudson/tasks/Shell/config.groovy

@@ -25,6 +25,5 @@ package hudson.tasks.Shell;
 f=namespace(lib.FormTagLib)
 
 f.entry(title:_("Command"),description:_("description",rootURL)) {
-    // TODO JENKINS-23151 'codemirror-mode': 'shell' is broken
-    f.textarea(name: "command", value: instance?.command, class: "fixed-width")
+    f.textarea(name: "command", value: instance?.command, class: "fixed-width", 'codemirror-mode': 'shell', 'codemirror-config': "mode: 'text/x-sh'")
 }

core/src/main/resources/lib/form/textarea/textarea.js

@@ -10,7 +10,8 @@ Behaviour.specify("TEXTAREA.codemirror", 'textarea', 0, function(e) {
         }
         
         var h = e.clientHeight || getTextareaHeight();
-        var config = e.getAttribute("codemirror-config") || "";
+        var config = e.getAttribute("codemirror-config");
+        config += (config ? ", " : " ") + "onBlur: function(editor){editor.save()}";
         config = eval('({'+config+'})');
         var codemirror = CodeMirror.fromTextArea(e,config);
         e.codemirrorObject = codemirror;