CPlusPlus: Proliferate FilePath use

The starts with CppDocument::filePath(), plus a bit of the fallout

This is one patch of potentially many. It is hard to draw the
line where to stop this kind of chunk, this here converts a few
additional functions for which including it in the patch looked
like less churn than without.

Converting is mostly fromString/toString, with a few exceptions
for "already seem" like caches, that use cheaper "path()" to
avoid likely performance regressions (on Windows FilePath
comparison is currently case-insenstive, and more expensive).

There should be no difference for local operation with this patch.

Change-Id: I7b35f98a0a6f0bfed4ea0f8f987faf586f7a8f2b
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/cppeditor/baseeditordocumentprocessor.h

@@ -10,6 +10,7 @@
 #include "cpptoolsreuse.h"
 
 #include <coreplugin/helpitem.h>
+
 #include <texteditor/codeassist/assistinterface.h>
 #include <texteditor/quickfix.h>
 #include <texteditor/texteditor.h>
@@ -18,7 +19,6 @@
 #include <cplusplus/CppDocument.h>
 
 #include <QTextEdit>
-
 #include <QVariant>
 
 #include <functional>
@@ -45,7 +45,7 @@ class CPPEDITOR_EXPORT BaseEditorDocumentProcessor : public QObject
     Q_OBJECT
 
 public:
-    BaseEditorDocumentProcessor(QTextDocument *textDocument, const QString &filePath);
+    BaseEditorDocumentProcessor(QTextDocument *textDocument, const Utils::FilePath &filePath);
     ~BaseEditorDocumentProcessor() override;
 
     void run(bool projectsUpdated = false);
@@ -65,7 +65,7 @@ public:
 
     virtual QFuture<CursorInfo> cursorInfo(const CursorInfoParams &params) = 0;
 
-    QString filePath() const { return m_filePath; }
+    const Utils::FilePath &filePath() const { return m_filePath; }
 
 signals:
     // Signal interface to implement
@@ -94,7 +94,7 @@ private:
     virtual void runImpl(const BaseEditorDocumentParser::UpdateParams &updateParams) = 0;
 
 private:
-    QString m_filePath;
+    Utils::FilePath m_filePath;
     QTextDocument *m_textDocument;
 };