[image_picker] Add the ability to pick multiple videos - platform implementations

[stuartmorgan-g]

Platform implementation portion of #9775

This adds support for the new getMultiVideoWithOptions method to all implementation packages.

Part of flutter/flutter#102283
Fixes flutter/flutter#146400

Pre-Review Checklist

• 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.
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• I updated/added any relevant documentation (doc comments with ///).
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• All existing and new tests are passing.

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Code Review

This pull request adds the ability to pick multiple videos by introducing the getMultiVideoWithOptions method. The feature is implemented across Android, iOS, web, Linux, and macOS platforms. The changes include necessary native code modifications, Dart API implementations, updates to example applications to demonstrate the new functionality, and additions to the test suites to ensure correctness. A significant refactoring was also done in the iOS implementation to unify the picker launching logic. The overall implementation is solid, but I found a minor issue in one of the new tests.