add collection_methods_unrelated_type

[devoncarew]

• added collection_methods_unrelated_type to core (available since 2.19)
• removed iterable_contains_unrelated_type from core (deprecated in 3.1)
• removed list_remove_unrelated_type from core (deprecated in 3.1)

See also dart-lang/core#798.

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[devoncarew]

Closing this - will follow up with one adding the new accepted lints.