Reduce image resolution by default in PDF Export

PDF Files can quickly become very big when a user inserts some images. Most users don't know how to reduce the size of their images.
This patch enables the resolution reduction for PDF Export to 300DPI by default.

Change-Id: I3ce5191de35561b59169e52e2e2efbc4a343f025
Reviewed-on: https://gerrit.libreoffice.org/8422Tested-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>

filter/source/pdf/pdfexport.cxx

@@ -106,7 +106,7 @@ PDFExport::PDFExport( const Reference< XComponent >& rxSrcDoc,
     mbExportHiddenSlides        ( sal_False ),
     mnOpenBookmarkLevels        ( -1 ),
     mbUseLosslessCompression    ( sal_False ),
-    mbReduceImageResolution     ( sal_False ),
+    mbReduceImageResolution     ( sal_True ),
     mbSkipEmptyPages            ( sal_True ),
     mbAddStream                 ( sal_False ),
     mnMaxImageResolution        ( 300 ),

officecfg/registry/schema/org/openoffice/Office/Common.xcs

@@ -5001,7 +5001,7 @@
               <desc>Specifies if the resolution of each image is reduced to the
               resolution specified by the property MaxImageResolution.</desc>
             </info>
-            <value>false</value>
+            <value>true</value>
           </prop>
           <prop oor:name="MaxImageResolution" oor:type="xs:int" oor:nillable="false">
             <info>