Allow users to re-enable browser-native contextmenu

[tmcw]

mapbox-gl-js version:

Steps to Trigger Behavior

1. Optionally call map.off('contextmenu')
2. Right-click on the map.

Expected Behavior

The browser's context menu will appear.

Actual Behavior

The _onContextMenu handler still prevents the event from having a default action.

[lucaswoj]

This came up in user testing. It is frustrating for new users to be unable to open devtools on a page with a full screen map. Our example code creates a fullscreen map.

[mourner]

It is frustrating for new users to be unable to open devtools on a page with a full screen map.

Other ways to open a devtools page (just in case anyone is struggling with the above):

• Options (on the right of the url tab) -> More Tools -> Developer Tools
• View -> Developer -> Developer Tools
• Option-Command-J

[jplante]

So right now the Mapbox Map does not allow right-clicking to open up the context-menu?

[initialdmg]

While this will make preserveDrawingBuffer invalid. If dragRotate is disabled, the context menu will display when click on the map, which indicates user to save the picture of the map.