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/libs/cplusplus/pp-engine.cpp

@@ -31,6 +31,7 @@
 #include <cplusplus/cppassert.h>
 
 #include <utils/executeondestruction.h>
+#include <utils/filepath.h>
 #include <utils/scopedswap.h>
 
 #include <QDebug>
@@ -235,7 +236,6 @@ struct Value
 };
 
 } // namespace Internal
-} // namespace CPlusPlus
 
 using namespace CPlusPlus;
 using namespace CPlusPlus::Internal;
@@ -251,7 +251,7 @@ Macro *macroDefinition(const ByteArrayRef &name,
                        unsigned bytesOffset,
                        unsigned utf16charsOffset,
                        unsigned line,
-                       Environment *env,
+                       CPlusPlus::Environment *env,
                        Client *client)
 {
     Macro *m = env->resolve(name);
@@ -320,7 +320,7 @@ class ExpressionEvaluator
     void operator = (const ExpressionEvaluator &other);
 
 public:
-    ExpressionEvaluator(Client *client, Environment *env)
+    ExpressionEvaluator(Client *client, CPlusPlus::Environment *env)
         : client(client), env(env), _lex(nullptr)
     { }
 
@@ -726,6 +726,14 @@ Preprocessor::Preprocessor(Client *client, Environment *env)
 {
 }
 
+QByteArray Preprocessor::run(const Utils::FilePath &filePath,
+                             const QByteArray &source,
+                             bool noLines,
+                             bool markGeneratedTokens)
+{
+    return run(filePath.toString(), source, noLines, markGeneratedTokens);
+}
+
 QByteArray Preprocessor::run(const QString &fileName,
                              const QByteArray &source,
                              bool noLines,
@@ -2158,3 +2166,5 @@ void Preprocessor::maybeStartOutputLine()
     if (*ch == '\\')
         buffer.append('\n');
 }
+
+} // namespace CPlusPlus