[accessibility] Activating a button using a keyboard should not set focus to the map element

[Malvoz]

When a button is activated using keyboard, the focus is set to the map element:

Leaflet.EasyButton/src/easy-button.js

Line 193 in cd53db5

this._map && this._map.getContainer().focus();

This is not the standard behavior of activating buttons, and is problematic because a keyboard-only user will have to tab through all the content to get back to the previously focused element if they wish to continue to explore the user interface.

[Malvoz]

Other potentially helpful resources:

• Leaflet Guideline: Test your maps
• Leaflet Plugin Authoring Guide: Content Accessibility