Relay ATTR_MEDIA_POSITION and ATTR_MEDIA_POSITION_UPDATED_AT in universal media_player

[michaelarnauts]

Description:
Universal media_player returns ATTR_MEDIA_POSITION and ATTR_MEDIA_POSITION_UPDATED_AT from it's active child now.

Related issue (if applicable): fixes #5060

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[mention-bot]

@michaelarnauts, thanks for your PR! By analyzing the history of the files in this pull request, we identified @balloob, @rmkraus and @fabaff to be potential reviewers.