Simplify embeddability test.

There is no reason to read the whole OS/2 table, and no need to spell
out the full names of all the types over and over.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2256783002

Review-Url: https://codereview.chromium.org/2256783002
diff --git a/src/sfnt/SkOTTable_OS_2.h b/src/sfnt/SkOTTable_OS_2.h
index 4a09a78..4382578 100644
--- a/src/sfnt/SkOTTable_OS_2.h
+++ b/src/sfnt/SkOTTable_OS_2.h
@@ -18,11 +18,11 @@
 #pragma pack(push, 1)
 
 struct SkOTTableOS2 {
-    static const SK_OT_CHAR TAG0 = 'O';
-    static const SK_OT_CHAR TAG1 = 'S';
-    static const SK_OT_CHAR TAG2 = '/';
-    static const SK_OT_CHAR TAG3 = '2';
-    static const SK_OT_ULONG TAG = SkOTTableTAG<SkOTTableOS2>::value;
+    static constexpr SK_OT_CHAR TAG0 = 'O';
+    static constexpr SK_OT_CHAR TAG1 = 'S';
+    static constexpr SK_OT_CHAR TAG2 = '/';
+    static constexpr SK_OT_CHAR TAG3 = '2';
+    static constexpr SK_OT_ULONG TAG = SkOTTableTAG<SkOTTableOS2>::value;
 
     union Version {
         SK_OT_USHORT version;