fix: dispose player implementation

[Gustl22]

Description

The implementation to dispose a player on the native side was missing for many platforms.

Checklist

• The title of my PR starts with a [Conventional Commit] prefix (fix:, feat:, docs:, chore: etc).
• I have read the [Contributor Guide] and followed the process outlined for submitting PRs.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation and added dartdoc comments with ///, where necessary.
• I have updated/added relevant examples in [example].

Breaking Change

• Yes, this is a breaking change.
• No, this is not a breaking change.

Related Issues

See #1467 (comment)

[spydon]

That sounds bad, should we release 4.0.1 with this tomorrow maybe?

[Gustl22]

Yes, completely forgot about the dispose statement, which we didn't have before. So it should work as before after upgrading, but it's better for resources to be able to dispose the player, if not needed anymore.
We did have a dispose method, but not linked to the native players. So it would probably break for some users, if leave unfixed.