LibUnicode: Parse compact identifiers and replace them with a format key

For example, in en-US, the decimal, long compact pattern for numbers
between 10,000 and 100,000 is "00 thousand". In that pattern, "thousand"
is the compact identifier, and the generated format pattern is now
"{number} {compactIdentifier}". This also generates that identifier as
its own field in the NumberFormat structure.

Userland/Libraries/LibUnicode/Locale.h

@@ -122,6 +122,7 @@ struct NumberFormat {
     StringView zero_format {};
     StringView positive_format {};
     StringView negative_format {};
+    StringView compact_identifier {};
 };
 
 struct ListPatterns {