[video_player_platform_interface] upgraded to pigeon 1.0

[gaaclarke]

The code should behave the same except the wire format has been modified in Pigeon 1.0 to support nested types and multiple arguments.

This shouldn't merge until Pigeon 1.0 is published: flutter/packages#447

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

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[stuartmorgan-g]

We'll need to fix flutter/flutter#85391 before this can land unfortunately.

[stuartmorgan-g]

Per previous discussion offline, based on the new platform channel plan the approach for updating Pigeon in video_player is going to be to move the platform channel for iOS and Android into the implementation, and then update there. Since that's the direct we want to go with platform channels, doing it first will avoid the need for a breaking change to the current platform interface (both saving us unnecessary churn, and avoiding disruption to unendorsed implementations).