loplugin:unusedenumconstants in vcl

- drop TTCR_GLYPHSEQ
- drop ImageType::Invalid
- give preedit_data_t a default constructor, so my plugin spots that the
eState field is being initalised to DontKnow effectively by a memset
- document ToolbarIconSize::Small as unused, but can't remove since
it might be stored in a user-setting somewhere

Change-Id: I94b34bba83a04de16f95e4faec95b4bd29f3c652
Reviewed-on: https://gerrit.libreoffice.org/33887
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/unusedenumconstants.py

@@ -89,6 +89,7 @@ for d in definitionSet:
          "sw/source/filter/inc/wwstyles.hxx",
          "sw/source/filter/ww8/fields.hxx",
          "vcl/source/fontsubset/cff.cxx",
+         "include/vcl/settings.hxx", # stored in a setting, can't remove it without potentially triggering UBSAN
         # unit test code
          "cppu/source/uno/check.cxx",
         # general weird nonsense going on
@@ -97,6 +98,7 @@ for d in definitionSet:
         # Windows or OSX only
          "include/canvas/rendering/icolorbuffer.hxx",
          "include/vcl/commandevent.hxx",
+         "vcl/inc/unx/gendata.hxx",
         # must match some other enum
          "include/editeng/bulletitem.hxx",
          "include/editeng/svxenum.hxx",