Minecraft 1.13-pre8, Minecraft 1.13-pre9, Minecraft 1.13-pre10, Minecraft 1.13
Windows 10 Home (Build 17134.112)
Java x64 1.8.0u51
They appear in Japanese translation for "key.spectatorOutlines", "command.context.here", and so on.
A partial list of characters that could be displayed in 1.12.2 but not in 1.13:
(U+FF08, U+FF3B, U+FF5B, U+FF5C, U+FFE4)