ClangFormat: Change the logic how configuration is picked

Let's use by default the configuration that clang-format picks itself
for the source file. The Qt Creator configuration will now only
override the default one with global or project settings and can be
turned off with the checkbox.

This behavior is clearer than always picking some configuration
which Qt Creator prefers best.

Change-Id: If5ed3d67eb6b4b47a6d0fd5259f7efbb608914d1
Reviewed-by: Marco Bubke <marco.bubke@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

src/plugins/clangformat/clangformatsettings.h

@@ -25,6 +25,8 @@
 
 #pragma once
 
+#include <QString>
+
 namespace ClangFormat {
 
 class ClangFormatSettings
@@ -43,10 +45,14 @@ public:
 
     void setFormatOnSave(bool enable);
     bool formatOnSave() const;
+
+    void setOverrideDefaultFile(bool enable);
+    bool overrideDefaultFile() const;
 private:
     bool m_formatCodeInsteadOfIndent = false;
     bool m_formatWhileTyping = false;
     bool m_formatOnSave = false;
+    bool m_overrideDefaultFile = false;
 };
 
 } // namespace ClangFormat