[video_player_android] Platform view support

[FirentisTFW]

This PR adds support for platform views on Android as a way of displaying a video. When creating a video, it's now possible to choose between texture view approach (rendered using Texture widget on the Flutter side) and platform view approach (rendered on the native side, using SurfaceView).

VideoPlayer class now has nothing to do with texture. The texture-related code was moved from it to TextureBasedVideoPlayer - a subclass of VideoPlayer that adds texture functionality. In the plugin class (create method) we create either the basic version (for platform view) or the texture subclass (in case of texture approach) based on the parameter (viewType) passed in from Flutter side.

The functionality is not yet exposed in the app-facing package (only in the example app) - it will be done in a separate PR. The PR does not introduce breaking changes.

Related issues:

• #86613 - this issue requests platform view support for iOS. Here we also add it for the Android, so that it works on both mobile platforms.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to 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, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or this PR is exempt from CHANGELOG changes.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

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