tdf#131098 docx export: write fill property of graphic

All these are round-tripping (at least at a basic level):
- bitmap
- hatch
- solid color
- transparency (unit test)

make CppunitTest_sw_ooxmlexport21 \
    CPPUNIT_TEST_NAME=testTdf131098_imageFill

No existing unit tests had an image with a fill.

Change-Id: I745fa064db83bdb3bb7ec67eef1ae803f3930a23
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/168134
Reviewed-by: Justin Luth <jluth@mail.com>
Tested-by: Jenkins
diff --git a/sw/qa/extras/ooxmlexport/ooxmlexport21.cxx b/sw/qa/extras/ooxmlexport/ooxmlexport21.cxx
index 901a0b1..baeba73 100644
--- a/sw/qa/extras/ooxmlexport/ooxmlexport21.cxx
+++ b/sw/qa/extras/ooxmlexport/ooxmlexport21.cxx
@@ -534,9 +534,6 @@ DECLARE_OOXMLEXPORT_TEST(testTdf126533_pageBitmap, "tdf126533_pageBitmap.docx")

DECLARE_OOXMLEXPORT_TEST(testTdf131098_imageFill, "tdf131098_imageFill.docx")
{
    if (isExported())
        return;

    // given a document with an image background transparency (blue-white)
    CPPUNIT_ASSERT_EQUAL(drawing::FillStyle_GRADIENT,
                         getProperty<drawing::FillStyle>(getShape(1), "FillStyle"));
diff --git a/sw/source/filter/ww8/docxattributeoutput.cxx b/sw/source/filter/ww8/docxattributeoutput.cxx
index 971f27d..827d037 100644
--- a/sw/source/filter/ww8/docxattributeoutput.cxx
+++ b/sw/source/filter/ww8/docxattributeoutput.cxx
@@ -5411,6 +5411,10 @@ void DocxAttributeOutput::FlyFrameGraphic( const SwGrfNode* pGrfNode, const Size
    m_pSerializer->singleElementNS(XML_a, XML_avLst);
    m_pSerializer->endElementNS( XML_a, XML_prstGeom );

    m_rDrawingML.SetFS(m_pSerializer); // to be sure that we write to the right stream
    if (xShapePropSet)
        m_rDrawingML.WriteFill(xShapePropSet, awt::Size(aSize.Width(), aSize.Height()));

    const SvxBoxItem& rBoxItem = pFrameFormat->GetBox();
    const SvxBorderLine* pLeft = rBoxItem.GetLine(SvxBoxItemLine::LEFT);
    const SvxBorderLine* pRight = rBoxItem.GetLine(SvxBoxItemLine::RIGHT);