Ensure browser preview canvases don't get treated like map canvas

docks

They have their own special logic, and shouldn't respond to
any project based settings or triggers

Fixes #20362

(cherry picked from commit c54c559)

Author: nyalldawson

src/app/qgisapp.cpp

@@ -8181,7 +8181,15 @@ QList<QgsMapCanvasAnnotationItem *> QgisApp::annotationItems()
 
 QList<QgsMapCanvas *> QgisApp::mapCanvases()
 {
-  return findChildren< QgsMapCanvas * >();
+  // filter out browser canvases -- they are children of app, but a different
+  // kind of beast, and here we only want the main canvas or dock canvases
+  auto canvases = findChildren< QgsMapCanvas * >();
+  canvases.erase( std::remove_if( canvases.begin(), canvases.end(),
+                                  []( QgsMapCanvas * canvas )
+  {
+    return !canvas || canvas->property( "browser_canvas" ).toBool();
+  } ), canvases.end() );
+  return canvases;
 }
 
 void QgisApp::removeAnnotationItems()

src/gui/qgsbrowserdockwidget_p.cpp

@@ -121,6 +121,7 @@ QgsBrowserLayerProperties::QgsBrowserLayerProperties( QWidget *parent )
   mMetadataTextBrowser->setOpenLinks( false );
   connect( mMetadataTextBrowser, &QTextBrowser::anchorClicked, this, &QgsBrowserLayerProperties::urlClicked );
 
+  mMapCanvas->setProperty( "browser_canvas", true );
   mMapCanvas->setLayers( QList< QgsMapLayer * >() );
   mMapCanvas->setMapTool( new QgsMapToolPan( mMapCanvas ) );
   mMapCanvas->freeze( true );