[PlaylistPlayer] Resolve plugin paths to fill the item infotag

[basrieter]

Description

Backport for #16158:

When a plugin:// path is played for the first time from the jsonrpc API, there is no information stored in the database for the item and it does not contain any music or video infotags (item->IsAudio() || item->IsVideo() is false). That makes Kodi interpret the item as a playlist (g_application.PlayMedia) and information such as the item subtitles is not available. Users using remote control applications are not able to select the item provided subtitles. Subs will only be available the next time the item is played since at that moment the item info is already in the database and is filled by FillFileItemList. This PR makes sure the plugin path is resolved before checking if it is audio or video, solving the issue.

Motivation and Context

Fixes #16151

How Has This Been Tested?

With a proof of concept video plugin, changing the plugin:// play path to make sure it is always an unknown path not in the db. Played the item via Kore remote app and checked the option to select subtitles was available.

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed

[bigretromike]

I have similar issue with
xbmc.Player().play(url, listitem)
When url starts with plugin:// for the first time Player.GetItem() returns infovideotag, but when files is played again it does not return that info anymore.

Does this PR fix this issue ? (I initially think so, but I build kodi 20190604-75c1d6b3e7-dirty today from master and the issue is still there)

Any chance to port his to player also (or json-rpc)?