sc-perf: lock drawing layer during creation of captions for Save

This gives an extra boost compared to commit
451c4ccc (see there for further details)
as it eliminates broadcasts to accessibility and thus obtaining text forwarders
and what not.

ScPostIt::CreateCaptionFromInitData() compared to that commit
from 145,055,889,118
to    63,386,691,509

Overall ScDocShell::SaveXML() from original state before that commit
Before: 370,433,720,090
 After: 107,468,180,524

Reduced to 29% or speed-up by factor 3.45

Change-Id: Ife86476c9654739ed9adf25e775f7568ea9934c2

sc/source/filter/xml/xmlwrap.cxx

@@ -719,8 +719,22 @@ bool ScXMLImportWrapper::ExportToComponent(const uno::Reference<uno::XComponentC
 
 bool ScXMLImportWrapper::Export(bool bStylesOnly)
 {
+    // Prevent all broadcasting and repaints and notification of accessibility
+    // during mass creation of captions, which is a major bottleneck and not
+    // needed during Save.
+    ScDrawLayer* pDrawLayer = rDoc.GetDrawLayer();
+    bool bOldLock = bool();
+    if (pDrawLayer)
+    {
+        bOldLock = pDrawLayer->isLocked();
+        pDrawLayer->setLock(true);
+    }
+
     rDoc.CreateAllNoteCaptions();
 
+    if (pDrawLayer)
+        pDrawLayer->setLock(bOldLock);
+
     uno::Reference<uno::XComponentContext> xContext(comphelper::getProcessComponentContext());
 
     uno::Reference<xml::sax::XWriter> xWriter = xml::sax::Writer::create(xContext);