
This change adds support for triple click to select a paragraph at the clicked position and triple click + drag to extend the selection paragraph-by-paragraph when using the SelectionArea widget. This PR also: * Makes `Text` widgets a `SelectionContainer` if a parent `SelectionRegistrar` exists. * Fixes issues with selectable ordering involving `WidgetSpan`s. Fixes: https://github.com/flutter/flutter/issues/104552