In general, for uicontrol components you would use textwrap, but it doesn't work in App Designer.
Some of them, such as uibutton, have a property named WordWrap that you can set to 'on', but, to my knowledge, you can't do it with with uilistbox.
lbox = uilistbox('Items', {['This is a' newline 'long list name'], ...
'Short one', ...
'Short two', ...
'Short three'}, ...
'Position', [125 120 100 78]);
Result:
