Prevent 'mousedown' events within Select from closing Popovers.

[TomTirapani]

Prevent 'mousedown' events within Select from closing Popovers.
See issue #3516

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[lbwexler]

This is a great change. Do we think there are a number of workarounds in place that could be unwound? If so, I think we should mention this in changelog.

[TomTirapani]

Yeah, there’s definitely a few places in client apps where this could be carefully unwound. Will add a changelog entry when I get back to my desk.

[TomTirapani]

Added CHANGLOG

[lbwexler]

👍🏻 thanks Tom!