Allow override of tab select functionality

[vicky-holcomb]

Currently, when typing in dropdown field and tabbing/clicking out of the input field, if a value was previously focused/highlighted, that value is selected. Requesting the ability to override that functionality and not always select a focused value on tab out.

Note: In SimpleSelect, focusedOption should be reset in the constructor. Currently, any dropdown re-rendered on the same page already has a focused option and will select that on tab.