Generalize 3 functions to return length on success

Instead of a bool, they will now return the number of bytes that
comprise the character being checked.  So the result can be used as a
bool, just as before; or the extra information can save recalculations,
as done in the future commits.

Author: khwilliamson

embed.fnc

@@ -1753,17 +1753,17 @@ ATdip	|bool	|is_utf8_fixed_width_buf_loclen_flags			\
 				|NULLOK const U8 **ep			\
 				|NULLOK STRLEN *el			\
 				|const U32 flags
-CRp	|bool	|is_utf8_FOO_	|const U8 classnum			\
+CRp	|Size_t |is_utf8_FOO_	|const U8 classnum			\
 				|NN const U8 *p 			\
 				|NN const U8 * const e
 ARTdip	|bool	|is_utf8_invariant_string_loc				\
 				|NN const U8 * const s			\
 				|STRLEN len				\
 				|NULLOK const U8 **ep
-CRp	|bool	|is_utf8_perl_idcont_					\
+CRp	|Size_t |is_utf8_perl_idcont_					\
 				|NN const U8 *p 			\
 				|NN const U8 * const e
-CRp	|bool	|is_utf8_perl_idstart_					\
+CRp	|Size_t |is_utf8_perl_idstart_					\
 				|NN const U8 *p 			\
 				|NN const U8 * const e
 ARTdmp	|bool	|is_utf8_string |NN const U8 *s 			\

proto.h

@@ -3900,32 +3900,37 @@ S_warn_on_first_deprecated_use(pTHX_ U32 category,
 }
 #endif
 
-/* returns a boolean giving whether or not the UTF8-encoded character that
- * starts at <p>, and extending no further than <e - 1> is in the inversion
- * list <invlist>. */
-STATIC bool
+/* returns the number of bytes comprising the UTF8-encoded character that
+ * starts at <p>, and extending no further than <e - 1> if it is in the
+ * inversion list <invlist>; or 0 if it isn't */
+STATIC Size_t
 S_is_utf8_in_invlist(pTHX_ const U8 * p, const U8 * e, SV * const invlist)
 {
-    return _invlist_contains_cp(invlist, utf8_to_uv_or_die(p, e, NULL));
+    Size_t advance;
+    if (_invlist_contains_cp(invlist, utf8_to_uv_or_die(p, e, &advance))) {
+        return advance;
+    }
+
+    return 0;
 }
 
-bool
+Size_t
 Perl_is_utf8_FOO_(pTHX_ const U8 classnum, const U8 *p, const U8 * const e)
 {
     PERL_ARGS_ASSERT_IS_UTF8_FOO_;
 
     return S_is_utf8_in_invlist(aTHX_ p, e, PL_XPosix_ptrs[classnum]);
 }
 
-bool
+Size_t
 Perl_is_utf8_perl_idstart_(pTHX_ const U8 *p, const U8 * const e)
 {
     PERL_ARGS_ASSERT_IS_UTF8_PERL_IDSTART_;
 
     return S_is_utf8_in_invlist(aTHX_ p, e, PL_utf8_perl_idstart);
 }
 
-bool
+Size_t
 Perl_is_utf8_perl_idcont_(pTHX_ const U8 *p, const U8 * const e)
 {
     PERL_ARGS_ASSERT_IS_UTF8_PERL_IDCONT_;