[docs] Release note for JDK-8031485

JDK-8031485 is a known regression in AWT on Mac OS X, but it's already too late in the release cycle to fix it, so it should be described in the release note as a known issue.

Suggested text:
The ComboBox control is consuming the Esc and Enter keys, so when the ComboBox is focused in the Dialog it's impossible to use keyboard to close the dialog. Only Mac OS X platform is affected by this issue.