function navKey(keyChar, ctrlKey) {
    var result;
    if (keyChar.length > 1 || !this.editOnKeydown || ctrlKey) {
        result = keyChar; // return the mapped value
    }
    return result;
}
Returns any value of `keyChar` that passes the following logic test:
1. If a non-printable, white-space character, then nav key.
2. If not (i.e., a normal character), can still be a nav key if not editing on key down.
3. If not, can still be a nav key if CTRL key is down.

Note: Callers are typcially only interested in the following values of `keyChar` and will ignore all others:
* `'LEFT'` and `'LEFTSHIFT'`
* `'RIGHT'` and `'RIGHTSHIFT'`
* `'UP'` and `'UPSHIFT'`
* `'DOWN'` and `'DOWNSHIFT'`

@param {string} keyChar - A value from Canvas's `charMap`.
@param {boolean} [ctrlKey=false] - The CTRL key was down.
@returns {undefined|string} `undefined` means not a nav key; otherwise returns `keyChar`.
@memberOf module:defaults