- Add `300ms` delay for it to consider it as selection drag instead of
an attempt to make a new selection.
- Add cursor icon while dragging the selection.

This is same as what chromium does:
https://chromium.googlesource.com/chromium/blink/+/master/Source/core/input/EventHandler.cpp#142

Release Notes:

- Fixed issue where you accidentally end up dragging the selection where
intent was to make a new one instead. To drag selection now, you need to
hold just a little longer before dragging.