Removes the legacy analysis options for all `url_launcher` packages, and fixes all resulting violations. Most fixes are automatic `dart fix` changes.

No version change: Most of these changes are to code that don't affect clients, or are clearly no-ops (e.g., adding a type specifier that was already strongly inferred). Only the packages where there is some potential for change—although none is actually expected—have version bumps.

Part of https://github.com/flutter/flutter/issues/76229