Quadruple prime in Libertinus Math not honoring ssty feature

[Omikhleia]

Describe the bug

Libertinus Math has the quadruple prime (U+2057) glyph, but the latter is not covered by the ssty font feature which only handles the prime, double prime, triple prime and their reverse variants.

Steps to reproduce

Type all primes U+2032..U+2037 and U+2057 in Libertinus Math with +ssty enabled.

Expected vs. actual behavior

Expected all primes U+2032..U+2037 and U+2057 to be in "script size" -- Actually observed: the quadruple prime isn't.

Screenshots / logs

Additional context

Feature ssty is useful for MathML engines - See sile-typesetter/sile#2173