CLDR-18879 Update MessageFormat for v48 - Normative changes

Changes to REQUIRED parts of the specification:

- Require prioritising syntax & data model errors (#1011)
- Make the Default Bidi Strategy required and default (#1066)
- Rename `:math` as `:offset` and publish it as Stable (#1073)

Changes to OPTIONAL or Draft parts of the specification:

- Rebrand the format more clearly as "Unicode MessageFormat" (#1064)
- Refactor the pattern selection definition without changing its meaning (#1080)
- Update the `:datetime`, `:date`, and `:time` functions to build on semantic skeletons (#1078, #1083)
- Add `:percent` as a new Draft function (#1094)

Author: eemeli