Add ShiftJIS decode/encode support for MoarVM

This makes the new shiftjis support in MoarVM accessible. It is
accessible as windows-932 because that is the dialect of shiftjis that
was implemented. It is not listed as shiftjis to maintain forward
compatibility in case other shiftjis (or the original) are added in
later.

src/core/Encoding/Registry.pm6

@@ -19,6 +19,7 @@ my class Encoding::Registry {
             'latin1','latin-1','csisolatin1','l1','ibm819','cp819'),
           nqp::list('windows-1251', 'windows1251'),
           nqp::list('windows-1252', 'windows1252'),
+          nqp::list('windows-932', 'windows932')
         );
         my int $i = -1;
         my int $elems = nqp::elems($encodings);

src/core/Rakudo/Internals.pm6

@@ -299,6 +299,9 @@ my class Rakudo::Internals {
       # windows-1252
       'windows-1252',    'windows-1252',
       'windows1252',    'windows-1252',
+      # ShiftJIS
+      'windows-932',     'windows-932',
+      'windows932',      'windows-932',
     );
     method NORMALIZE_ENCODING(Str:D \encoding) {
         my str $key = nqp::unbox_s(encoding);