[libc++][chrono] Implements formatter day.

This implements the enabled specializaton
template<class charT> struct formatter<chrono::day, charT>;

and
template<class charT, class traits>
    basic_ostream<charT, traits>&
      operator<<(basic_ostream<charT, traits>& os, const day& d);

Implements:
- LWG 3241 chrono-spec grammar ambiguity in ยง[time.format]

Partially implements:
- P1361 Integration of chrono with text formatting

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D128577

NOKEYCHECK=True
GitOrigin-RevId: e5d2d3eafbb367450c4fb75d3ee72b3b4bba522b
diff --git a/include/module.modulemap.in b/include/module.modulemap.in
index 4898dae..cf1c7dd 100644
--- a/include/module.modulemap.in
+++ b/include/module.modulemap.in
@@ -492,29 +492,43 @@
     export *
 
     module __chrono {
-      module calendar              { private header "__chrono/calendar.h" }
-      module convert_to_timespec   { private header "__chrono/convert_to_timespec.h" }
-      module day                   { private header "__chrono/day.h" }
-      module duration              { private header "__chrono/duration.h" }
-      module file_clock            { private header "__chrono/file_clock.h" }
-      module hh_mm_ss              { private header "__chrono/hh_mm_ss.h" }
-      module high_resolution_clock {
+      module calendar               { private header "__chrono/calendar.h" }
+      module convert_to_timespec    { private header "__chrono/convert_to_timespec.h" }
+      module convert_to_tm          { private header "__chrono/convert_to_tm.h" }
+      module day                    { private header "__chrono/day.h" }
+      module duration               { private header "__chrono/duration.h" }
+      module file_clock             { private header "__chrono/file_clock.h" }
+      module formatter              {
+        @requires_LIBCXX_ENABLE_LOCALIZATION@
+        private header "__chrono/formatter.h"
+      }
+      module hh_mm_ss               { private header "__chrono/hh_mm_ss.h" }
+      module high_resolution_clock  {
         private header "__chrono/high_resolution_clock.h"
         export steady_clock
         export system_clock
       }
-      module literals              { private header "__chrono/literals.h" }
-      module month                 { private header "__chrono/month.h" }
-      module month_weekday         { private header "__chrono/month_weekday.h" }
-      module monthday              { private header "__chrono/monthday.h" }
-      module steady_clock          { private header "__chrono/steady_clock.h" }
-      module system_clock          { private header "__chrono/system_clock.h" }
-      module time_point            { private header "__chrono/time_point.h" }
-      module weekday               { private header "__chrono/weekday.h" }
-      module year                  { private header "__chrono/year.h" }
-      module year_month            { private header "__chrono/year_month.h" }
-      module year_month_day        { private header "__chrono/year_month_day.h" }
-      module year_month_weekday    { private header "__chrono/year_month_weekday.h" }
+      module literals               { private header "__chrono/literals.h" }
+      module month                  { private header "__chrono/month.h" }
+      module month_weekday          { private header "__chrono/month_weekday.h" }
+      module monthday               { private header "__chrono/monthday.h" }
+      module ostream                {
+        @requires_LIBCXX_ENABLE_LOCALIZATION@
+        private header "__chrono/ostream.h"
+      }
+      module parser_std_format_spec {
+        @requires_LIBCXX_ENABLE_LOCALIZATION@
+        private header "__chrono/parser_std_format_spec.h"
+      }
+      module statically_widen       { private header "__chrono/statically_widen.h" }
+      module steady_clock           { private header "__chrono/steady_clock.h" }
+      module system_clock           { private header "__chrono/system_clock.h" }
+      module time_point             { private header "__chrono/time_point.h" }
+      module weekday                { private header "__chrono/weekday.h" }
+      module year                   { private header "__chrono/year.h" }
+      module year_month             { private header "__chrono/year_month.h" }
+      module year_month_day         { private header "__chrono/year_month_day.h" }
+      module year_month_weekday     { private header "__chrono/year_month_weekday.h" }
     }
   }
   module codecvt {