Improves the touch-based text selection UI in text boxes.

With this change, when a user is in "text select" mode, they
can swipe any part of the text. This changes the behavior of
the touch-based select in 2 ways (behavior for cursor-based
select remains the same):

1. You can now indicate where your select will start. Before
this change, the select always started at the last cursor
position.

2. Selection will respect word boundaries. Before this
change the selection would be character to character. Since
users don't have a fine grain level of control over touch
events, this would often lead to incomplete selections.