Bug - MultiTypeaheadSelect template - toggle keyboard handling doesn't allow customization

[kmcfaul]

Specifically for MultiTypeaheadSelect, but maybe applies to other selects as well. The onKeyDown handler of the text input in the toggle has behavior set for the enter key but doesn't prevent the default behavior, and doesn't allow the user to override that if the menu is closed. If the menu is open, the user can hook into the event via onSelectionChange. We should either have the option of adding additional keyboard handling to this handler, or pass the event through onToggle.

Workaround - pass an onKeyDown handler to the outer menu toggle via toggleProps that has handling for the key (in this case enter).