LibUnicode: Parse and generate standard accounting formatting rules

Also known as "currency-accounting" in some CLDR documentation.

Userland/Libraries/LibUnicode/Locale.h

@@ -81,6 +81,7 @@ struct LocaleID {
 enum class StandardNumberFormatType : u8 {
     Decimal,
     Currency,
+    Accounting,
     Percent,
 };