Auto detect scrolling container

[luin]

Closes #2166, #3199, #1527, #2091, #2642

Changes:

• Auto detect scrolling container
• Quill#focus() accepts preventScroll option. A usage of this is in restoreFocus() in base.ts.
• Added Quill#scrollRectIntoView(). This makes developers easy to override Quill#scrollSelectionIntoView().

Improvements

1. Supported scrolling multiple ancestor scrolling container
2. Supported VisualViewport API so it works with works with mobile soft keyboard ([iOS 12] Quill editor does not scroll while typing. Cursor hidden under soft keyboard #2642).
3. Supported scrolling in both block and inline direction.
4. Supported scroll-padding CSS property to allow users customize the scrolling behavior.
5. Supported transform: scale(x).
6. Took borders, scrollbar sizes into consideration.