WOFF2 fonts are missing ligatures present in OTF fonts

[fionn]

With ligatures enabled, the OTF fonts render ligatures as expected but the WOFF2 fonts don't render with ligatures.

See https://fionn.github.io/libertinus-test/, where using liga, dlig and calt on v7.051 (latest release) it's clear that we're missing the Qu, tz, Th, fi and ch ligatures in the WOFF2 font.