perlguts: the type is Perl_OpDumpContext

which I missed in the review of #22572 but found when I tried to use
it.

Author: tonycoz

pod/perlguts.pod

@@ -3938,9 +3938,9 @@ I<oldop> is the previous OP optimized, whose C<op_next> points to I<o>.
 =item xop_dump
 
 This member is a pointer to a function of type
-C<void (pTHX_ OP *, struct OpDumpContext *)>. If set, this function is called
-by C<op_dump()> when dumping a custom operator of this type, after the op's
-basic fields have been printed. This function may make use of
+C<void (pTHX_ OP *, struct Perl_OpDumpContext *)>. If set, this function is
+called by C<op_dump()> when dumping a custom operator of this type, after
+the op's basic fields have been printed. This function may make use of
 C<opdump_printf()> to emit additional output that may be useful for debugging.
 
 The opaque structure pointer passed in as its final argument should be passed