Create a Tag from its numeric value, optionally with a name.
The returned object is frozen: a Tag is a value, as in the reference,
and a store keeps the tags it is given by identity when they are frozen.
Tag.from(1, "date");
Tag.from(12345);
Optionalname: string
Value-type companion for the
Taginterface: an interface plus a mergedconstwith a handful of members. It stays small and must not import the encode/format graph.