Revert "Attempt to remove deprecated uvuni_to_utf8()"

This reverts commit 463db48.

This caused HTML::Parser to break, and looking at the code, I realized
that I need to do more work before there is an acceptable alternative.

Closes #23521

Author: khwilliamson

embed.fnc

@@ -3870,6 +3870,8 @@ Admp	|U8 *	|uv_to_utf8_msgs|NN U8 *d				\
 				|UV uv					\
 				|UV flags				\
 				|NULLOK HV **msgs
+CDbp	|U8 *	|uvuni_to_utf8	|NN U8 *d				\
+				|UV uv
 EXdpx	|bool	|validate_proto |NN SV *name				\
 				|NULLOK SV *proto			\
 				|bool warn				\

embed.h

@@ -928,6 +928,7 @@
 #   define utf8_to_uvchr(a,b)                   Perl_utf8_to_uvchr(aTHX_ a,b)
 #   define utf8_to_uvuni(a,b)                   Perl_utf8_to_uvuni(aTHX_ a,b)
 #   define utf8n_to_uvuni(a,b,c,d)              Perl_utf8n_to_uvuni(aTHX_ a,b,c,d)
+#   define uvuni_to_utf8(a,b)                   Perl_uvuni_to_utf8(aTHX_ a,b)
 # endif
 # if defined(PERL_CORE)
 #   define PerlLIO_dup2_cloexec(a,b)            Perl_PerlLIO_dup2_cloexec(aTHX_ a,b)

mathoms.c

@@ -142,6 +142,14 @@ Perl_utf8_to_uvuni(pTHX_ const U8 *s, STRLEN *retlen)
     return NATIVE_TO_UNI(valid_utf8_to_uvchr(s, retlen));
 }
 
+U8 *
+Perl_uvuni_to_utf8(pTHX_ U8 *d, UV uv)
+{
+    PERL_ARGS_ASSERT_UVUNI_TO_UTF8;
+
+    return uvoffuni_to_utf8_flags(d, uv, 0);
+}
+
 /*
 =for apidoc_section $unicode
 =for apidoc utf8n_to_uvuni

pod/perldelta.pod

@@ -398,10 +398,6 @@ well.
 Removed the deprecated (since 5.32) functions C<sv_locking()> and
 C<sv_unlocking>.
 
-=item *
-
-Removed the deprecated (since 5.32) function C<uvuni_to_utf8()>
-
 =back
 
 =head1 Selected Bug Fixes