[Camera] Add lens type information (iOS)

[lenzpaul]

This PR adds lens type information. The goal is to identify whether the lens type is wide, ultra-wide, telephoto, etc., as discussed in flutter/flutter#119908. The iOS implementation is complete, so lens data will now be populated on iOS.

• Introduces a new CameraLensType enum to provide lens type information about the camera (e.g.: ultra-wide, telephoto, ...)
• Adds lensType in the PlatformCameraDescription and CameraDescription classes
• Implements utility functions to convert between PlatformCameraLensType and CameraLensType.
• Updates auto-generated code (using Pigeon) to reflect these changes.

Current CameraDescription for iPhone 11

[
    CameraDescription(
        com.apple.avfoundation.avcapturedevice.built-in_video:0,
        CameraLensDirection.back,
        90
    ),
    CameraDescription(
        com.apple.avfoundation.avcapturedevice.built-in_video:1,
        CameraLensDirection.front,
        90
    ),
    CameraDescription(
        com.apple.avfoundation.avcapturedevice.built-in_video:5,
        CameraLensDirection.back,
        90
    )
]

New CameraDescription for iPhone 11

[
    CameraDescription(
        com.apple.avfoundation.avcapturedevice.built-in_video:0,
        CameraLensDirection.back,
        90,
        CameraLensType.wide
    ),
    CameraDescription(
        com.apple.avfoundation.avcapturedevice.built-in_video:1,
        CameraLensDirection.front,
        90,
        CameraLensType.wide
    ),
    CameraDescription(
        com.apple.avfoundation.avcapturedevice.built-in_video:5,
        CameraLensDirection.back,
        90,
        CameraLensType.ultraWide
    )
]

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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