Problems:
HTML's native <button> tag doesn't support flex styling in all browsers,
causing layout bugs. And buttons or links created by "createDOMElement"
(without an accessibility role) do not have the correct props.
Solution:
The "button" role is rendered to a "div[role=button]" that is focusable
and responds to the same keyboard events as a native button. A native
button can still be rendered using "createDOMElement".
Make "createDOMProps" aware of the component context to ensure style
resets and other props are correctly applied when an accessibility role
is not defined.
Additionally:
This patch also adds a new "label" role to support accessible forms.
It maps to a native label element.
Close#241
* Change 'accessible' to align with React Native.
* Add support for 'importantForAccessibility'.
* Stop event propagation for keyboard-activated Touchables (nested
Touchables now respond the same as when touch-activated).
* Fix whitespace layout of nested Text elements.
* Use 'div' for Text to improve TalkBack grouping.
* Rewrite accessibility docs.
Close#382Fix#408
