Switch to using portabl gsize/gssize instead of size_t/ssize_t

Switch to using portabl gsize/gssize instead of size_t/ssize_t

Original commit message from CVS:
* gst/gstregistrybinary.c: (gst_registry_binary_write),
(gst_registry_binary_read_cache):
* gst/gstregistryxml.c: (gst_registry_save):
* gst/gsturi.c: (unescape_string), (gst_uri_has_protocol):
* plugins/elements/gstfilesink.c: (gst_file_sink_open_file):
* plugins/elements/gstfilesrc.c: (gst_file_src_map_region),
(gst_file_src_map_small_region), (gst_file_src_create_mmap):
Switch to using portabl gsize/gssize instead of size_t/ssize_t
Fixes #520152