Restore PUA math alphabets from STIX 1

[davidmjones]

STIX version 1 contains two math alphabets that are not (yet?) encoding by Unicode and that were inadvertently dropped in STIX Two:

• sans-serif italic Greek alphabet (U+E1B4–E1F6)
• and italic double struck alphabet (U+E154–E17C)

They should be restored.

[kenmcd]

This can be closed. All of these are in STIX Two Math v2.11 in the PUA in the same locations.