riff: add support for nikon tags

Nikon cameras store metadata in a custom format. Add parsing of the chunk and
extract some initial data.
API: gst_riff_parse_ncdt()
Fixes #636143
riff: fix indentation messup from previous commit
win32: export new riff api
riff: remove new parse_ncdt api again

This chunk is avi specific, no need to expose this as public api.
typefind: add support of BWF RF64  a 64bit wav variant

Detect and describe the RF64 Broadcast Wave Format.
Fixes #519220