playbin3/decodebin3/parsebin : Fix various subtitles issues

commit 3693b079 (HEAD -> main) Author: Edward Hervey edward@centricular.com Date: Tue Feb 20 16:04:09 2024 +0100

playbin3: Inform (uri)decodebin3 of the subtitle caps from playsink

Subtitles are better handled by overlayers/renderers within playsink. By
informing (uri)decodebin3 of the formats that can be handled we can avoid those
being "decoded" too early.

Fixes #1081

commit 01655585 Author: Edward Hervey edward@centricular.com Date: Tue Feb 20 16:02:25 2024 +0100

parsebin: Use pbutils utils to identify more stream types

Handles all cases provided they are identified in the pbutils descriptions
list.

Fixes #1081

commit 82adef8c Author: Edward Hervey edward@centricular.com Date: Tue Feb 20 16:00:07 2024 +0100

subparsers: Give proper category to subtitle "decoders"

Some subtitle "decoders" had a wrong category of "Parser", which `parsebin`
relies on to identify elements which do not *decode* streams but *parse* them.

This would cause such subtitle decoders to be plugged in within parsebin,
preventing the original stream to be properly used by (more efficient)
downstream decoders or subtitle renderers.

Fixes #1757

Fixes #1081 (closed) Fixes #1757 (closed)