[camera_web] Migrate to package:web

[Rexios80]

Fixes flutter/flutter#139748

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
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• 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.
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• 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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