Warn for PropTypes that don't exist but do exist with a different case

[aweary]

Original issue: facebook/react#6153

[katsos]

Is anyone working on this one? I'd like to contribute.

@aweary can you please provide me the copy to display when the prop-type doesn't exist?

[lukescott]

Isn't #11 somewhat related? If you warned about every property that wasn't defined, wouldn't that highlight onaction as not defined? You could also look for similar cases though to provide a better error message - did you mean 'onAction'?.

[aladh]

@lukescott A warning about different capitalization would be useful in any scenario, as it is most likely a typo. The issue mentioned in #11 does overlap, but seems like it should be opt-in.

[ljharb]

This seems like something that React itself would have to do. Separately, PropTypes.exact can catch all these typos by warning on any unrecognized prop.