Fix bug #11860 with displaying composite RTL characters on MS-Windows.

Fix bug #11860 with displaying composite RTL characters on MS-Windows.

 src/w32uniscribe.c (uniscribe_shape): Fix producing gstring
 components for RTL text.  Adjust X-OFFSET of each non-base glyph
 for the width of the base character, according to what
 x_draw_composite_glyph_string_foreground expects.  Generate
 WADJUST value according to composition_gstring_width's
 expectations, to produce correct width of the composed character.
 Reverse the sign of the DU offset produced by ScriptPlace.