support `injectJavaScript`

[LonelyCpp]

Hi, I've been trying to get better support for RNWeb for react-native-youtube-iframe

A major drawback is the lack of injectJavaScript method.

I will try to raise an MR to add this if possible. Any suggestions would be helpful :)

[jeanniton-mnr]

injectedJavaScript the documentation failed to mention that JavaScript codes are only injected when loading local html code.

You can look at the library code.