Enforce unicode entries with an optional build flag

[dzuk-mutant]

This is an option I'd like to have open in case I restructure the Mutant Standard project. Basically some kind of build flag that (a bit like how -q enforces resolution) requires all emoji entries have a valid unicode codepoint entry, otherwise it will refuse to build.

[dzuk-mutant]

Back then, I wanted this when PUA codepoints were more important to me, now they are not, I don't see the point of this anymore.