FilePath: Avoid QStringView::first, which is only available in Qt 6

but FilePath is still used with sdktool = qt 5.15.2

Change-Id: Ibb196411fc37efc74db6df4ab024ac98db6cf4ea
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/libs/utils/filepath.cpp

@@ -342,7 +342,7 @@ QStringView FilePath::host() const
 
 QStringView FilePath::pathView() const
 {
-    return QStringView(m_data).first(m_pathLen);
+    return QStringView(m_data).left(m_pathLen);
 }
 
 QString FilePath::path() const