[webview_flutter_platform_interface] - Added limitsNavigationsToAppBoundDomains to WebSettings

[GauteHaugen]

Added limitsNavigationsToAppBoundDomains that is an optional setting for iOS 14+.

PR is the first PR replacement of #4339

List which issues are fixed by this PR. You must list at least one issue.
(flutter/issues/89530)

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed 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.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

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[stuartmorgan-g]

Sorry for the churn, but based on your latest update in the main PR I don't think we have a clear picture of what the implementation should actually look like after all, so I'm going to close this for now; I think there's a good chance we'll end up wanting something different at this layer by the time that discussion resolves.

Once we have an end-to-end design that works for the creation-time-only version, we can re-split a platform interface PR.