When triple clicking on text, we should select the entire paragraph, or
entire line in <input>s and <textarea>s. If the mouse button is held
down and the user starts dragging, the selection expands with additional
paragraphs or lines.
This expands on the work of Kai Wildberger (PR #7681) but was adjusted
for the work that happened previously to support double click + drag
moves and includes triple click support for our Qt UI.
Co-authored-by: Kai Wildberger <kiawildberger@gmail.com>
In EventHandler, we now keep track of a mouse selection mode which is
either None, Character or Word. By double clicking a word and
immediately dragging, you can now extend the selection word by word
instead of by character.
Instead of defining somewhat high level mouse actions, allow granular
control of mouse clicks and mouse down/up/move events. We will want to
simulate things like holding down a mouse button after double clicking
and then dragging the mouse to another position in the future, and this
enables that.
