[utils] Drop componentPropType in favor of PropTypes.elementType

[eps1lon]

Breaking change

-import { componentPropType } from '@material-ui/utils';
+import PropTypes from 'prop-types';

SomeComponent.propTypes = {
- component: componentPropType,
+ component: PropTypes.elementType,
}

Switched the wording from Component to element type in the docs. This is more in line with the flow types and now prop-types.

[oliviertassinari]

PropTypes.elementType was introduced in 15.7.0. Can we lose a bit the version requirement?
https://github.com/facebook/prop-types/blob/master/CHANGELOG.md

[eps1lon]

We already had 15.7.1 in the lockfile anyway and 15.7.2 had an important bug fix for browserify build. I would rather propagate that to downstream packages. The only time this would cause duplication (assuming this was bad) is when someone actually pins their prop-types to "prop-types": "15.7.1" and I don't see any reason for that.

[oliviertassinari]

Ok, I was looking for potential dependency deduplication for our users.

[eps1lon]

That can always happen which is why I always review lockfiles and adjust them if I see deduplication potential. I think both viewpoints are perfectly valid but I would insist in this case because 15.7.2 had a critical bug fix.

[oliviertassinari]

reactjs/react-docgen#330