Try to generate a beforeInput event for buggy composition scenarios in IE

[robbertbrak]

This PR attempts to fix facebookarchive/draft-js#695.

The Sogou Wubi Chinese IME does not always produce composition or input events in IE, particularly when typing full-width punctuation in a contentEditable div. I tried to work around this by marking the keyDown event that initiates the 'pseudo-composition' and handling the corresponding keyUp if it is not handled in the normal manner.

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[gaearon]

Sorry your PR was never addressed. I'm compiling a list of issues and unreviewed PRs in #11097 and we'll take a look at yours as soon as we can.

[robbertbrak]

Thanks @gaearon! As this was a while ago, it's worth checking whether this is still an issue with newer versions of Sogou Wubi.

[robbertbrak]

@gaearon: I just checked it again with a fresh install of Sogou Wubi. Unfortunately the issue is still present.

[gaearon]

Which versions of IE is this relevant for?

[gaearon]

Does this only happen for IE11, or is this relevant for Edge users as well?

[gaearon]

I'm going to close because there's not enough information for me to make a decision. If this only affects IE11 I don't think we'll be fixing this. If it affects Edge as well, we can reconsider.