LibUnicode: Precompute the compact scale of each number formatting rule

This will be needed for the ComputeExponentForMagnitude AO for compact
formatting, namely step 5b:

  Let exponent be an implementation- and locale-dependent (ILD) integer
  by which to scale a number of the given magnitude in compact notation
  for the current locale.

Userland/Libraries/LibUnicode/Locale.h

@@ -103,6 +103,7 @@ struct NumberFormat {
     };
 
     u8 magnitude { 0 };
+    u8 compact_scale { 0 };
     Plurality plurality { Plurality::Other };
     StringView zero_format {};
     StringView positive_format {};