sc, VmlFormControlExporter: avoid OStringBuffer style

It's more efficient to have just one big statement with all the + operations.

See
<https://gerrit.libreoffice.org/c/core/+/118488/2#message-425f5c995c78ed24df430154bec28d89dcef9eb3>.

Change-Id: Ifc304a58f5e34e7654a800fe1163beeec3f791a5
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/118635
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins
diff --git a/sc/source/filter/excel/xeescher.cxx b/sc/source/filter/excel/xeescher.cxx
index 2f92384..144782d 100644
--- a/sc/source/filter/excel/xeescher.cxx
+++ b/sc/source/filter/excel/xeescher.cxx
@@ -1151,14 +1151,11 @@ void VmlFormControlExporter::EndShape(sal_Int32 nShapeElement)
            break;
    }
    pVmlDrawing->startElement(FSNS(XML_x, XML_ClientData), XML_ObjectType, aObjectType);
    OString aAnchor = OString::number(m_aAreaFrom.Left());
    aAnchor += ", " + OString::number(m_aAreaFrom.Top());
    aAnchor += ", " + OString::number(m_aAreaFrom.Right());
    aAnchor += ", " + OString::number(m_aAreaFrom.Bottom());
    aAnchor += ", " + OString::number(m_aAreaTo.Left());
    aAnchor += ", " + OString::number(m_aAreaTo.Top());
    aAnchor += ", " + OString::number(m_aAreaTo.Right());
    aAnchor += ", " + OString::number(m_aAreaTo.Bottom());
    OString aAnchor
        = OString::number(m_aAreaFrom.Left()) + ", " + OString::number(m_aAreaFrom.Top()) + ", "
          + OString::number(m_aAreaFrom.Right()) + ", " + OString::number(m_aAreaFrom.Bottom()) + ", "
          + OString::number(m_aAreaTo.Left()) + ", " + OString::number(m_aAreaTo.Top()) + ", "
          + OString::number(m_aAreaTo.Right()) + ", " + OString::number(m_aAreaTo.Bottom());
    XclXmlUtils::WriteElement(pVmlDrawing, FSNS(XML_x, XML_Anchor), aAnchor);

    if (!m_aMacroName.isEmpty())