Issue #3104

Closes #2581

Closes #2858

We're still targeting ES3.

Add a dummy ContentEditableInput

Issue #3095

Issue #3089

Both to the annotateScrollbar and to the editor itself.

To prevent scrolling artifacts

Closes #2323

...  for getting information about collapsed spans

Issue #3079

So that the helper mechanism can meaningfully be used to register
asynchronous linters.

Use host property, not root.

Easiest to see the difference on touch-enabled device. Go to Tern demo
page (link below), click on a variable name and press Ctrl+I. Now pan
the editor's content. The tooltip stays at a fixed position, whilst
the variable name detaches and moves off.

The fix listens to scroll and blur, switching the tooltip off.

Issue #3055

Issue #3039

Opening the documentation in the same window navigates away from the
code editor.

So that the CodeMirror.Pass it will return actually ends up in the editor.

Closes #3040