Rewrite ARRAY_LENGTH as a template function

Such it wouldn't apply to pointers accidentally.
diff --git a/src/hb-ot-shape-complex-arabic-table.hh b/src/hb-ot-shape-complex-arabic-table.hh
index df85086..c66111b 100644
--- a/src/hb-ot-shape-complex-arabic-table.hh
+++ b/src/hb-ot-shape-complex-arabic-table.hh
@@ -914,9 +914,9 @@
 #define SHAPING_TABLE_LAST	0x06D3
 
 
-static const struct {
+static const struct ligature_set_t {
  uint16_t first;
- struct {
+ struct ligature_pairs_t {
    uint16_t second;
    uint16_t ligature;
  } ligatures[4];