ProjectExplorer: Handle project file list globally

Handle the generation of the list of files in a project globally, based
on the project tree.

Creator now has the concept of TreeManagers which can enrich the project
tree with additional data (e.g. the files found in a resource file), which
the project does not necessarily know about. So use that tree to find
the files that belong to a project instead of implementing similar features
in each project.

Change-Id: Ia375a914a1f2c0adaa427f9eda834eec2db07f68
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Marco Benelli <marco.benelli@qt.io>

src/plugins/qmlprojectmanager/qmlproject.h

@@ -51,7 +51,6 @@ public:
     bool supportsKit(ProjectExplorer::Kit *k, QString *errorMessage) const override;
 
     Internal::QmlProjectNode *rootProjectNode() const override;
-    QStringList files(FilesMode fileMode) const override;
 
     bool validProjectFile() const;
 
@@ -66,7 +65,6 @@ public:
     void refresh(RefreshOptions options);
 
     QDir projectDir() const;
-    QStringList files() const;
     QString mainFile() const;
     QStringList customImportPaths() const;
 
@@ -92,10 +90,7 @@ private:
     void parseProject(RefreshOptions options);
 
     QmlImport m_defaultImport;
-    ProjectExplorer::Target *m_activeTarget = 0;
-
-    // plain format
-    QStringList m_files;
+    ProjectExplorer::Target *m_activeTarget = nullptr;
 
     QPointer<QmlProjectItem> m_projectItem;
 };