* Manual roll of Dart 40fd1c456e...7e8348f4ce

dart-lang/sdk@7e8348f4ce [dart2js] Assume `isPotentialSubtype` is always true.
dart-lang/sdk@5671730c5a [dart2js] Pass type arguments to callable properties even with --omit-implicit-checks.
dart-lang/sdk@4c74ebb367 [benchmark] Add dartdevc-null targets.
dart-lang/sdk@56708696a9 [vm/nnbd/bytecode] Distinguish function types with different nullabilities in bytecode generator
dart-lang/sdk@d2f7039e9c [dart:io] Parse scoped IPv6 in constructor of InternetAddress
dart-lang/sdk@c2d28d1569 Rename Null Safety tests.
dart-lang/sdk@4d3ec06277 Add more data and performance operations for Cider.
dart-lang/sdk@3103d859e4 Remove unused TypeSystemImpl.mostSpecificTypeArgument().
dart-lang/sdk@6d9a4f16dd Issue 42757. Implement null spread element typing with null-safety.
dart-lang/sdk@8c316a99de Remove unnecessary null checks.
dart-lang/sdk@6c9b885e57 Remove StrongModeCode.INVALID_PARAMETER_DECLARATION; it's redundant
dart-lang/sdk@b98eb386ea [ddc] Use prebuilt_dart_action to build js
dart-lang/sdk@8796382840 Analyzer: Move invalid_super_invocation to compile-time error
dart-lang/sdk@cece303eb4 Check diagnostics in List/Map/SetLiteralTest(s).
dart-lang/sdk@cc519b9a03 Test that during partial resolution for Cider we don't resolve some nodes.
dart-lang/sdk@4ea6d6e130 [tests/ffi] Re-enable commented out tests
dart-lang/sdk@2225b6f472 Migration: fix handling of async functions that return FutureOr.
dart-lang/sdk@f907e561c9 Migration: never produce a type of the form `FutureOr<T?>?`.
dart-lang/sdk@69ba6e5f80 Make FileSystemEntity.absolutePath understand more Windows paths.
dart-lang/sdk@202e32afeb [vm] Native API: Introduce Dart_FinalizableHandle
dart-lang/sdk@debb4dddea [co19] Language/Types and Language/Variables tests enabled
dart-lang/sdk@3661464297 [infra] Update checked-in SDKs to 2.10.0-0.0.dev
dart-lang/sdk@b8dc7627a9 [cfe] Handle NullCheck in constant evaluation

* Switch Android windows builds to also use clang.

* Bump buildroot version to fe3b46e595e7ce1350e11aa0c90365976051f4a3

* Update license.