Search backwards with a Shift + Enter keyboard shortcut

Is your feature request related to a problem? Please describe.
Searching backwards with a keyboard shortcut. Right now you can only search forward by clicking "Enter", but it is common to search backwards with "Shift + Enter".

Describe the solution you'd like
Add a keyboard shortcut to searchBox.tx, for example:

if (event.shiftKey && event.keyCode === enterKey) {
  this.props.prev(event.currentTarget.value);
} else if (event.keyCode === enterKey) {
  this.props.next(event.currentTarget.value);
}

Describe alternatives you've considered
Clicking the "find previous" button in the search bar, but that requires a lot of effort and annoying when I'm using the "Enter" shortcut and want to go backwards.

Additional context
N/A

Start in the searchBox.tx file named in the issue and inspect how the Enter key and the find-previous control are handled. Add the requested Shift + Enter behavior and verify that Enter still searches forward while Shift + Enter searches backward.