This is a continuation of the previous commit.
Calling initialize() is the first thing that's done after allocating a
cell on the JS heap - and in the common case of allocating an object,
that's where properties are assigned and intrinsics occasionally
accessed.
Since those are supposed to live on the realm eventually, this is
another step into that direction.
Intl.NumberFormat is meant to format both Number and BigInt types. To
prepare for formatting BigInt types, this generalizes our NumberFormat
implementation to operate on Value instances rather than doubles. All
arithmetic is moved to static helpers that can now be updated with
BigInt semantics.
There is quite a lot to be done here so this is just a first pass at
number formatting. Decimal and percent formatting are mostly working,
but only for standard and compact notation (engineering and scientific
notation are not implemented here). Currency formatting is parsed, but
there is more work to be done to handle e.g. using symbols instead of
currency codes ("$" instead of "USD"), and putting spaces around the
currency symbol ("USD 2.00" instead of "USD2.00").
