API: add GST_SEGMENT_FORMAT, which is a printf extension we register that lets us easily dump GstSegments into debug ...

Original commit message from CVS:
* configure.ac:
* docs/gst/gstreamer-sections.txt:
* gst/gstconfig.h.in:
* gst/gstinfo.c: (_gst_debug_init), (gst_debug_print_segment),
(_gst_info_printf_extension_ptr),
(_gst_info_printf_extension_segment):
API: add GST_SEGMENT_FORMAT, which is a printf extension we
register that lets us easily dump GstSegments into debug
logs (#350419).
* tests/check/gst/gstinfo.c: (segment_printf_extension_log_func),
(info_segment_format_printf_extension), (gst_info_suite):
Add simple unit test that logs a bunch of different segments (not
valgrinded at the moment because of leaks in gst_debug_add_log_function).