ComponentLifecycle is intended to provide some methods to Component
subclasses and enforce that overrides of those methods are correct in
those same subclasses.
However, it does neither of these things as an interface that
Component `implements`. It just checks that Component has all the
required methods of ComponentLifecycle. Since there are no required
methods, the `implements` check passes. And since Component doesn't
actually *implement* any of the methods, its subclasses don't get
them by default, and their 'overrides' are not checked for
correctness.
Changing ComponentLifecycle to a class fixes both of these problems.
* Use specific event type for nativeEvent property
Allows event handlers to fully use the `ev.nativeEvent` property without casting. But it does make the `React.MouseEvent` type slightly more complicated.
* Maintain backwards compatibility of SyntheticEvent type
TypeScript 2.3 should be adding type parameter defaults, which allows the `nativeEvent` property to be made generic but without breaking existing code.
* Override nativeEvent in the more specific event types
Overriding nativeEvent in this way maintains backwards compatibility and doesn't depend on bleeding-edge TypeScript features.
