Utils: Centralize FilePath case sensitivity handling

This could or possibly should the target device's file name case
sensitivity into account by diverting to IDevice. However, as this is
expensive and we are in time-critical path here, we go with "good
enough" for now.

The first approximation is "Anything unusual is not case sensitive"
which is better than "Any device equals the host".

Change-Id: Ib3d4a627abebd96a7285a855af66e0c800767767
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/fileutils.h

@@ -146,6 +146,8 @@ public:
     bool isDir() const;
     bool isNewerThan(const QDateTime &timeStamp) const;
 
+    Qt::CaseSensitivity caseSensitivity() const;
+
     FilePath relativeChildPath(const FilePath &parent) const;
     FilePath relativePath(const FilePath &anchor) const;
     FilePath pathAppended(const QString &str) const;