SMUFL 8/15 clef variants not used

[dbenjaminmiller]

Bravura should have all the clefs listed here, with an 8/15 baked into the clef for various examples (both above and below): https://www.w3.org/2021/03/smufl14/tables/clefs.html

[ed.] Per documentation, none of these are used, but only in the case of treble_8 is the appearance equivalent to what SMUFL would normally do, so this would be good to implement:

\version "2.25.0"
ekmFont = "Bravura"
ekmUse = "12 english"
\include "cosmufl.ily" 
\language "english"

\book{
\score{
<<
\new Staff \with {
} \fixed c' { \clef "treble"
\time 6/8 a4 b4 c'4
\cueClef "treble_8" a,4 b,4 c4
\cueClef "treble^8" a'4 b'4 c''4
\cueClef "bass_8" a,,4 b,,4 c,4
\cueClef "bass^8" a4 b4 c'4 \break
\cueClefUnset
\time 6/8 a4 b4 c'4
\clef "treble_8" a,4 b,4 c4
\clef "treble^8" a'4 b'4 c''4
\clef "bass_8" a,,4 b,,4 c,4
\clef "bass^8" a4 b4 c'4

}
>>
\layout{}
}}