[dart2wasm] Move list implementations to their own library

This WasmArray-backed list classes to `dart:_list`, similar to
`dart:_string` and `dart:_typed_data`

This will allow having internally-public list members like unchecked
getters and setters that we will use in the rest of the standard
library.

This CL doesn't add anything new, just renames things.

- `dart.core._ListBase` -> `dart._list.WasmListBase`

  This is to avoid confusion with `dart.core.ListBase` (defined by Dart
  standard library), and also to be consistent with `WasmTypedDataBase`
  and `WasmStringBase`.

- `dart.core._List` -> `dart._list.ModifiableFixedLengthList`

  Similar to the above, to avoid confusion with `dart.core.List`.

- `GrowableList.ofOther` -> `GrowableList.fromIterable`

  `ofOther` sounds like it should make a growable list from another
  growable list, but the type is more general than that. To reflect what
  it actually does we call it `fromIterable`.

Tested: Existing tests.
Change-Id: I24398765e1b0d549fc70b03ba94161479c5fc54c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/372622
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>