SH-4274 FIX Adding RegionHandshakeReply flags for SSA

Adding a flag to hint to the sim that this viewer knows how to handle
AvatarAppearance messages for self in SSA-enabled regions.

Upstream patch: 5fdc790f6d

indra/newview/llviewerregion.h

@@ -56,6 +56,8 @@
 #define WATER 2
 const U32	MAX_OBJECT_CACHE_ENTRIES = 50000;
 
+// Region handshake flags
+const U32 REGION_HANDSHAKE_SUPPORTS_SELF_APPEARANCE = 1U << 2;
 
 class LLEventPoll;
 class LLVLComposition;