Add refrain and versicle symbols

[lasconic]

SMuFL is missing Versicle ℣ (U+2123) and Response (Refrain) ℟ (U+211F). These symbols are used in responsorial psalms apparently.
Maybe it has been considered but abandoned since they are in Unicode already. I'm not sure what the policy is. Can someone clarify?

References

• See measure 39 http://www.mutopiaproject.org/ftp/NaujalisJ/O7/naujalis-popule-meus/naujalis-popule-meus-let.pdf
• https://www.romanliturgy.org/?p=41
• https://musescore.org/en/node/44816

[mscuthbert]

I considered suggesting it when we did the med-ren areas, since they're very common, but because they were also in Unicode, I didn't. They're good to have in the SMuFL range because they interact with musical symbols, but they generally match the metrics of a text font, so I wouldn't, for instance, use the SMuFL code point if my lyric font had these symbols in them.