Deprecate $num_points parameter of image(open|filled)polygon

Cf. <https://wiki.php.net/rfc/deprecations_php_8_1#num_points_parameter_of_image_open_filled_polygon>.

Co-authored-by: Máté Kocsis <kocsismate@woohoolabs.com>
Co-authored-by: George Peter Banyard <7906688+Girgias@users.noreply.github.com>

Closes GH-6789.

UPGRADING

@@ -370,6 +370,9 @@ PHP 8.1 UPGRADE NOTES
   . The filter.default ini setting is deprecated.
     RFC: https://wiki.php.net/rfc/deprecations_php_8_1
 
+- GD:
+  . The $num_points parameter of image(open|filled)polygon has been deprecated.
+
 - Hash:
   . The mhash(), mhash_keygen_s2k(), mhash_count(), mhash_get_block_size() and
     mhash_get_hash_name() functions are deprecated. Use the hash_*() APIs

ext/gd/gd.c

@@ -2726,6 +2726,8 @@ static void php_imagepolygon(INTERNAL_FUNCTION_PARAMETERS, int filled)
 			RETURN_THROWS();
 		}
 		NPOINTS /= 2;
+	} else {
+		php_error_docref(NULL, E_DEPRECATED, "Using the $num_points parameter is deprecated");
 	}
 
 	im = php_gd_libgdimageptr_from_zval_p(IM);

ext/gd/tests/bug55005.phpt

@@ -14,6 +14,9 @@ trycatch_dump(
     fn () => imagepolygon($g, array(200,10, 200,100, 280,100), 2, $fgnd)
 );
 ?>
---EXPECT--
+--EXPECTF--
+Deprecated: imagefilledpolygon(): Using the $num_points parameter is deprecated in %s on line %d
 !! [ValueError] imagefilledpolygon(): Argument #3 ($num_points_or_color) must be greater than or equal to 3
+
+Deprecated: imagepolygon(): Using the $num_points parameter is deprecated in %s on line %d
 !! [ValueError] imagepolygon(): Argument #3 ($num_points_or_color) must be greater than or equal to 3