Consider using WasmArrays in maps and related data structures

[mkustermann]

In dart2wasm we currently use VM's base implementation for linked hash maps (_HashFieldBase with various mixins). The VMs implementation uses Uint32List for the index and non-growable List<Object?> for the data. This means means a map object in wasm consists actually of 5 objects we can reduce that to 3 objects by using WasmArray<>s for index + data. This also avoids extra cost on the indirect access.

The downside is we depart from sharing the code with VM, but we can still use shared mixins and try to keep in sync in their implementation.

There's associated data structures, e.g. iterators, that are similarly affected

/cc @osa1

[osa1]

WIP in https://dart-review.googlesource.com/c/sdk/+/354843.