[platform-ui-dev] Deprecating IDialogConstants.BUTTON_HEIGHT

[Billy Biggs <vektor@xxxxxxxxxxxx>]

  JFace currently uses a constant number of dialog units for button
height.  This causes problems on platforms which have buttons that are
larger than on Windows, either with a larger border or added padding
outside of buttons.  An example of this is bug 68568, where certain GTK+
themes add enough padding to make buttons unreadable using JFace's hint.

  A good cross-platform solution that still uses dialog units is
challenging, since the concept does not fit well under GTK+ and MacOS X.
Instead, I have checked in code which stops using the BUTTON_HEIGHT
constant in favour of just using the default height from SWT.  This
seems to fix the problem, removes code, and does not seem to adversely
affect dialog layout in other ways.

  Please let me know if this causes problems or unpleasing layouts.  If
this goes well in M2 I would like to deprecate the constant.

  -Billy