ProjectExplorer: Rename IncludePathType to HeaderPathType

It is the type used by the HeaderPath class, so reflect that in
the name.

I also considered to rename HeaderPath to IncludePath, but
that name is reflected in a lot of users, which would also need
to be adjusted for consistency. That would blow up the patch size
for little value IMHO.

Change-Id: I51421dbd3ab8b2874dc32fc82dc394c9b93ce5e9
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangcodemodel/test/clangautomationutils.cpp

@@ -96,7 +96,7 @@ static const ProjectExplorer::HeaderPaths toHeaderPaths(const QStringList &paths
 {
     ProjectExplorer::HeaderPaths result;
     foreach (const QString &path, paths)
-        result.push_back({path, ProjectExplorer::IncludePathType::User});
+        result.push_back({path, ProjectExplorer::HeaderPathType::User});
     return result;
 }