CMake: Fix includes all over the CMake plugin

Keep internals internal, remove some unnecessary includes, add
some that should have been there.

This reduces the number of files that get rebuild when working
on CMake internals from over 1000 to about 200.

This patch also moves some code around that ended up being
in the wrong file.

Change-Id: Icd7366ac760dc85031040720418fbb16336dce9b
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cmakeprojectmanager/cmakeprojectplugin.h

@@ -25,21 +25,21 @@
 
 #pragma once
 
-#include "cmakespecificsettingspage.h"
-
 #include <extensionsystem/iplugin.h>
 
 namespace CMakeProjectManager {
 namespace Internal {
 
-class CMakeProjectPlugin : public ExtensionSystem::IPlugin
+class CMakeSpecificSettings;
+
+class CMakeProjectPlugin final : public ExtensionSystem::IPlugin
 {
     Q_OBJECT
     Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QtCreatorPlugin" FILE "CMakeProjectManager.json")
 
 public:
     static CMakeSpecificSettings *projectTypeSpecificSettings();
-    ~CMakeProjectPlugin() override;
+    ~CMakeProjectPlugin();
 
 #ifdef WITH_TESTS
 private slots:
@@ -60,8 +60,8 @@ private slots:
 #endif
 
 private:
-    bool initialize(const QStringList &arguments, QString *errorMessage) override;
-    void extensionsInitialized() override;
+    bool initialize(const QStringList &arguments, QString *errorMessage);
+    void extensionsInitialized();
 
     void updateContextActions();