[browser][wasm] Configuring request options in Browser WebAssembly

[kjpou1]

Initial implementation of request options used by Browser WebAssembly.

See proposal: #34168

namespace System.Net.Http
{
    public readonly struct HttpRequestOptionsKey<TValue>
    {
        public HttpRequestOptionsKey(string key);
        public string Key { get; }
    }
    public sealed class HttpRequestOptions : IDictionary<string, object>
    {
        // Explicit interface implementation
        public bool TryGetValue<TValue>(HttpRequestOptionsKey<TValue> key, out TValue value);
        public void Set<TValue>(HttpRequestOptionsKey<TValue> key, TValue value);
    }
    public class HttpRequestMessage : IDisposable
    {
        [Obsolete("Use Options instead.")]
        public IDictionary<string, object> Properties => Options;

        public HttpRequestOptions Options { get; }
    }
}

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[stephentoub]

I started going through the PR, but it doesn't appear to match the approved API. I'll hold off reviewing further until that's resolved. Thanks.

[kjpou1]

@marek-safar @stephentoub is this ready?

[stephentoub]

@scalablecory and/or @geoffkizer, can you review while I'm out? thanks.

[lewing]

This looks ok to me now, can we get a review from libraries/networking

[kjpou1]

Could someone from libraries/networking give this a look over? @scalablecory and/or @geoffkizer

[karelz]

@geoffkizer can you please help with code review here on behalf of ncl? Thanks!

[geoffkizer]

I haven't been part of the design discussions so I'm just assuming we're all happy with the design as approved -- with that said, code looks good to me.

[kjpou1]

Thanks @geoffkizer