…-mansion#412)

Fixes the issue we encountered software-mansion#406 (comment)

To review, the problem is as follows:

The correct syntax is:

```
static propTypes = {
    ...GenericTouchable.internalPropTypes
}
```

Metro/Babel compiles this to:

```
// Define GenericTouchable
GenericTouchable.propTypes = (0, _objectSpread2.default)({}, GenericTouchable.internalPropTypes, GenericTouchable.publicPropTypes);
```

But when metro then runs the HMR transform, this becomes:

```
// Create _class
_class.propTypes = (0, _objectSpread2.default)({}, GenericTouchable.internalPropTypes, GenericTouchable.publicPropTypes),
```

It rewrites the class name to `_class` during initialization, but misses the references in the spread, which then causes a undefined-access exception.

See this Gist for full outputs: https://gist.github.com/miracle2k/3bc7f1c50080397dbf0d92cfb3101677#file-generictouchable-babel-with-metro-preset-js

Part of the problem seems to be that metro uses a very old version of [react-hot-loader](facebook/metro#336).

The code as it is currently in the library, using `...this.publicPropTypes` has two problems: First, it does not compile at all with babel, when this library becomes imported as part of using `react-native-web`.

Second, while it does compile using metro, the generated code instead will be:

```
// Create _class
_class.propTypes = (0, _objectSpread2.default)({}, this.internalPropTypes, this.publicPropTypes),
```

With `this` probably referring to the window or global scope, thus not causing a crash, but not actually setting the proptypes correctly.