[MacPorts] #53350: fontconfig: support mpgk/mdmg packaging

[MacPorts]

#53350: fontconfig: support mpgk/mdmg packaging
------------------------+------------------------
 Reporter:  ctreleaven  |      Owner:  ryandesign
     Type:  defect      |     Status:  new
 Priority:  Normal      |  Milestone:
Component:  ports       |    Version:
 Keywords:              |       Port:  fontconfig
------------------------+------------------------
 Patch adds a postinstall script, etc, that mimics the existing post-
 activate step (which initializes or updates the font cache).

 fontconfig is used by a variety of packages including libass, libbluray,
 qt5-qtbase, qt5-qtwebkit among others.  Thus this script will propogate to
 any installer incorporating any of these packages.

 Tested by creating and installing an mpkg of fontconfig.  Installer log
 attached showing successful completion.

--
Ticket URL: <https://trac.macports.org/ticket/53350>
MacPorts <https://www.macports.org/>
Ports system for macOS