A layout manager which can layout like-heighted components in a grid
pattern based on their preferred sizes. Can be used in packed or unpacked
mode. Column positions are based on the preferred sizes of the first row
of components.
When packed, the components are sorted from narrowest to widest;
subsequent rows will use these columns, with components two wide for a
single column spanning two or more columns.
When not packed, the components are sorted from widest to narrowest,
resulting in more whitespace, but consistent rows of columns - no
component will span more than one column.
Used by RadioInplaceEditor
to manage the set of radio
buttons representing property editor tags.