ProjectExplorer: Replace Node::setNodeType by virtual functions

Not the usual direction of change, but currently there are
several systems to identify or invoke node functionality.

Virtual functions are likely to stay in this context, so this
here attempts to help consolidation by reducing the influence
of the node type flags, hopefully leading to full removal
by making remaining functionality available through the
other mechanisms (virtual functions, asFooNode() 'casts',
less so the FileType flag).

Change-Id: I12a17ce30b3c8883995b29b4720408020ee0fa3e
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/projectexplorer/projectnodes.cpp

@@ -165,7 +165,16 @@ Node::~Node() = default;
 
 NodeType Node::nodeType() const
 {
-    return m_nodeType;
+    if (isFileNodeType())
+        return NodeType::File;
+    if (isFolderNodeType())
+        return NodeType::Folder;
+    if (isProjectNodeType())
+        return NodeType::Project;
+    if (isVirtualFolderType())
+        return NodeType::VirtualFolder;
+    QTC_CHECK(false);
+    return NodeType::File;
 }
 
 int Node::priority() const
@@ -308,11 +317,6 @@ FileType Node::fileTypeForFileName(const Utils::FileName &file)
                                                       Utils::MimeMatchMode::MatchExtension));
 }
 
-void Node::setNodeType(NodeType nodeType)
-{
-    m_nodeType = nodeType;
-}
-
 /*!
   \class ProjectExplorer::FileNode
 
@@ -434,7 +438,6 @@ QString FileNode::displayName() const
 */
 FolderNode::FolderNode(const Utils::FileName &folderPath)
 {
-    setNodeType(NodeType::Folder);
     setFilePath(folderPath);
     setPriority(DefaultFolderPriority);
     setListInProject(false);
@@ -793,7 +796,6 @@ bool FolderNode::showWhenEmpty() const
 VirtualFolderNode::VirtualFolderNode(const Utils::FileName &folderPath) :
     FolderNode(folderPath)
 {
-    setNodeType(NodeType::VirtualFolder);
 }
 
 QString VirtualFolderNode::addFileFilter() const
@@ -819,7 +821,6 @@ QString VirtualFolderNode::addFileFilter() const
 ProjectNode::ProjectNode(const Utils::FileName &projectFilePath) :
     FolderNode(projectFilePath)
 {
-    setNodeType(NodeType::Project);
     setPriority(DefaultProjectPriority);
     setListInProject(true);
     setDisplayName(projectFilePath.fileName());
@@ -930,7 +931,6 @@ void FolderNode::handleSubTreeChanged(FolderNode *node)
 ContainerNode::ContainerNode(Project *project)
     : FolderNode(project->projectDirectory()), m_project(project)
 {
-    setNodeType(NodeType::Project);
 }
 
 QString ContainerNode::displayName() const