refactor!: remove FallThroughError before deletion in Dart 3

[Lyokone]

Description

The API FallThroughError is deprecated and scheduled for dart-lang/sdk#49529.

Replacing with Exception

Related Issues

closes #10079

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[dcharkes]

Drive by comment (as I seem to have made a PR for the same issue). Is the change from Error to Exception intended? I chose UnsupportedError error instead.

See: Exceptions are recoverable, errors are not.

[Lyokone]

@dcharkes Thanks we were discussing this internally, and I hadn't updated my PR yet. I'll close it in favor of yours.

[mit-mit]

New PR is #10087