Mirrors the SDK's formulaSeparatorsForDecimal (calculation/compiler/FormulaSeparators), which is
internal to the engine. This is the presentation side of the same rule, and it is only ever used to
BUILD text that is then re-parsed and validated before it replaces anything (see
formatEvalLiteral's note) — so a drift between the two degrades F9 to a no-op rather than
writing a formula the engine can't read.
The formula separators a user of this locale types, keyed off the locale's decimal point — Excel's rule: a comma decimal pushes the argument/column separator to
;and rows to the one remaining character.