Adds double click to select a word.
Adds double click + drag to select word by word.

https://user-images.githubusercontent.com/948037/234363577-941c36bc-ac42-4b7f-84aa-26b106c9ff05.mov

Partially fixes #104552

This change updates `SelectableRegion`s right-click gesture to match native platform behavior.

Before: Right-click gesture selects word at position and opens context menu (All Platforms)
After: 
- Linux, toggles context menu on/off, and collapses selection when click was not on an active selection (uncollapsed).
- Windows, Android, Fuchsia, shows context menu at right-clicked position (unless the click is at an active selection).
- macOS, toggles the context menu if right click was at the same position as the previous / or selects word at position and opens context menu.
- iOS, selects word at position and opens context menu.

This change also prevents the `copy` menu button from being shown when there is a collapsed selection (nothing to copy).

Fixes #117561

* Support keyboard selection in selectable region

* fix some comments

* addressing comments

* Use `curly_braces_in_flow_control_structures` for `rendering`

* fix comments

* fix dangling

* Support global selection

* addressing comments

* add new test

* Addressing review comments

* update

* addressing comments

* addressing comments

* Addressing comments

* fix build