Reposition hidden textarea to work around Chrome IME issue

Chrome would show the IME widget too high because it noticed the textarea
was cut off by the wrapping DIV.

Issue #4095

lib/codemirror.js

@@ -1221,7 +1221,7 @@
   };
 
   function hiddenTextarea() {
-    var te = elt("textarea", null, null, "position: absolute; padding: 0; width: 1px; height: 1em; outline: none");
+    var te = elt("textarea", null, null, "position: absolute; bottom: -1em; padding: 0; width: 1px; height: 1em; outline: none");
     var div = elt("div", [te], null, "overflow: hidden; position: relative; width: 3px; height: 0px;");
     // The textarea is kept positioned near the cursor to prevent the
     // fact that it'll be scrolled into view on input from scrolling