Resolve a NumberFormatRef to a format-code string.
Strings pass through; built-in ids resolve via the ECMA table (unknown ids
resolve to 'General', matching Excel's behavior for unmapped ids).
Parameters
ref: NumberFormatRef
Returns string
Remarks
Locale-ADAPTIVE rendering of ids 14/22 is a value-level concern
handled before engines format (see toLocaleDateCore) — this function
always returns the canonical code.
Resolve a Ref to a format-code string.