[camera_avfoundation] Wrappers swift migration - part 2

[RobertOdrowaz]

Migrates camera wrappers as part of flutter/flutter#119109

This PR migrates wrappers to Swift:

• FLTCameraDeviceDiscovering
• FLTDeviceOrientationProviding

In line with Swift conventions, the FLT prefixes are removed. The Default class implementations are replaced with protocol conformance on base AV classes.

Pre-Review 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.
• 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 I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

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Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩↩²↩³

[gemini-code-assist]

Code Review

This pull request continues the migration of the camera_avfoundation plugin from Objective-C to Swift by converting FLTCameraDeviceDiscovering and FLTDeviceOrientationProviding. The changes involve replacing Objective-C protocols and implementations with their Swift equivalents, updating call sites to use the new Swift types, and removing the now-obsolete Objective-C files. The new Swift code follows modern conventions, such as using computed properties instead of methods where appropriate. I've left one comment regarding a naming inconsistency for you to consider. Overall, this is a solid step forward in the migration process.