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 codemirror#4095

Author: marijnh

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