Add musical symbols for unicode completions (#54182)
I found that julia was missing some useful music notation unicode
completions and sometimes [had to copy and paste these unicodes to use
the published
package](https://github.com/JuliaMusic/MusicTheory.jl/issues/27).
So I picked out some unicode music symbols that might be useful, named
from the [unicode
standard](https://www.unicode.org/charts/PDF/U1D100.pdf).
I didn't add the test, I don't think it's necessary.
Thanks for reviewing. Please reply if any changes are needed.
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Co-authored-by: Lilith Orion Hafner <lilithhafner@gmail.com>
