gsttaglist: Add new tag GST_TAG_RFC6381_CODECS

Submitted by Yeongjin Jeong

Created attachment 371566
Suggests adding the following new tags: GST_TAG_RFC6381_CODECS.

Suggests adding the following new tags: GST_TAG_RFC6381_CODECS.

This is useful for information which creates Live streaming protocol metadata such as M3U8 master playlist or MPD manifest.

Becase, some media player framework such as MSE (Media Source Extensions) need more information 'rfc6381-codecs' to test support for in the current browser.
=> https://developer.mozilla.org/en-US/docs/Web/API/MediaSource/isTypeSupported

Also I uploaded patches that push rfc6381-codecs tag in hlsdemuxer and dashdemuxer.

Patch 371566, "Suggests adding the following new tags: GST_TAG_RFC6381_CODECS.":
0001-gsttaglist-Add-new-tag-GST_TAG_RFC6381_CODECS.patch

Version: 1.14.0