Register whether a glyph run goes from RTL or LTR

Register whether a glyph run goes from RTL or LTR

This is needed by scene graph when embedding text objects in
RTL text. Since the number of flags required for
QGlyphRun is increasing, I've also refactored the
underline/overline/strikethrough settings to use a common
QFlags interface.

Task-number: QTBUG-20917
Change-Id: I070649c014f4a51cfd66a9579d2d221a8f22302f
Reviewed-on: http://codereview.qt-project.org/5739
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jiang Jiang <jiang.jiang@nokia.com>