[util] Add --text-before and --text-after to hb-shape / hb-view

Use with Arabic, for example, to see the effect on joining.
diff --git a/util/hb-ot-shape-closure.cc b/util/hb-ot-shape-closure.cc
index 6dce7a1..2289605 100644
--- a/util/hb-ot-shape-closure.cc
+++ b/util/hb-ot-shape-closure.cc
@@ -61,7 +61,9 @@
   }
   void consume_line (hb_buffer_t  *buffer,
 		     const char   *text,
-		     unsigned int  text_len)
+		     unsigned int  text_len,
+		     const char   *text_before,
+		     const char   *text_after)
   {
     hb_set_clear (glyphs);
     shaper.shape_closure (text, text_len, font, buffer, glyphs);