Yet another fix for copying properties by 'format'

Yet another fix for copying properties by 'format'

* src/textprop.c (extend_property_ranges): Accept an additional
argument OLD_END, and only extend the end of a property range if
its original end is at OLD_END; all the other ranges are left
intact.  (Bug#23897)
* src/editfns.c (styled_format): Pass the original length of the
string to 'extend_property_ranges'.
* src/intervals.h (extend_property_ranges): Adjust prototype.

* test/src/editfns-tests.el (format-properties): Add tests for
bug#23897.