High and Low previously accepted only arrays and strings. They now
also accept any ordinal type — Integer, Int64, UInt32, UInt64,
SmallInt, Word, Byte, Boolean, and enums — as either a type name or
an expression. The result type matches the argument type so
High(Int64) round-trips through 64-bit code paths without truncation.
Bounds are folded at compile time to a literal QBE copy.
Floating-point arguments now produce a targeted error message
("not defined for floating-point types; use MaxDouble/MinDouble or
Math.Infinity") instead of the generic "must be an array or string".
docs/language-rationale.adoc records the decision; docs/grammar.ebnf
is updated to reflect the broadened intrinsic signatures.
aeb3e4ae8d