title: Determine if unicode character has a glyph in UIFont
body: <p>I want to find out if a certain unicode character has a glyph representation even if by a cascading font.  For example, let's say I am using <code>UIFont.systemFont(withSize:18)</code> and a string <code>\u{1CDA}</code> and would like to find out if this font will display the graphical representation of this character, and not a default question mark representation (ie there's no graphical representation, even by the supporting cascade fonts).</p>