C++: change working-copy to work on UTF-8 encoded QByteArrays.

These not only take less space than UTF-16 encoded QStrings, but due to
the caching in the CppEditorSupport also take less time to build.

This patch also fixes a number of possible encoding issues, where files
and constant strings were (falsely) assumed to be UTF-8.

Change-Id: Ib6f91c9a94ebed5b5dfbd4eb2998825c62c72784
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/cpptools/cpptoolseditorsupport.h

@@ -96,7 +96,7 @@ public:
 
     QString fileName() const;
 
-    QString contents() const;
+    QByteArray contents() const;
     unsigned editorRevision() const;
 
     void setExtraDiagnostics(const QString &key,
@@ -173,7 +173,7 @@ private:
     QFuture<void> m_documentParser;
 
     // content caching
-    mutable QString m_cachedContents;
+    mutable QByteArray m_cachedContents;
     mutable int m_cachedContentsEditorRevision;
     bool m_fileIsBeingReloaded;