[Feature request] Serif Greek and double-struck italic letters from the Private Use Area

[KuznetsovAleksey]

Description

STIX Two Math font contains upright and italic Greek letters in the Private Use Area "DE17C-"DE1B3, "DE1BE-"DE1F5 as well as italic double-struck letters in "DE154-"DE17B. Is it possible to implement Greek ranges inside the symsf and symsfit ranges and extend the symbbit range to associate letters from the PUA with them?

• Relevant for XeTeX
• Relevant for LuaTeX