HexDigits grammar needs update

[waldemarhorwat]

The current proposal correctly replaces HexDigits with CodePointDigits in some places but then still calls MV (and TRV) on the nonexistent HexDigits, without defining it on CodePointDigits. Please update the grammar and semantics to define those and fix the remaining references to HexDigits as appropriate.

[rwaldron]

Thanks for the heads up!