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)
Linked issues
is duplicated by 8
Attachments
Comments 7
Also, ')' (U+FF09), '{' (U+FF5B) and '}' (U+FF5D), see MC-133506
Duplicated by MC-134299
Can confirm for Minecraft 1.13-pre8