New FeatureCollection constructor for initialCapacity

[NinoFloris]

Background and Motivation

Some background can be found here, dictionary resizes were fairly visible in traces #31240

Proposed API

namespace Microsoft.AspNetCore.Http.Features
{
    public class FeatureCollection
    {
+       public FeatureCollection(int initialCapacity);
    }
}

Usage Examples

Initial place this will be used is

        public DefaultHttpContext()
            : this(new FeatureCollection(10)) // right here
        {
            Features.Set<IHttpRequestFeature>(new HttpRequestFeature());
            Features.Set<IHttpResponseFeature>(new HttpResponseFeature());
            Features.Set<IHttpResponseBodyFeature>(new StreamResponseBodyFeature(Stream.Null));
            // At least some slots left before resize for storing RequestAborted feature, Services and other such things. 
        }

The initial capacity of 10 is just an example, say 5 or 7 would also be fine for me.

Alternative Designs

This could also be handled through an internal constructor.

Risks

It can be viewed as api bloat if it provides minimal overall value.

[davidfowl]

API looks good to me. We'll review it in API review.

[mkArtakMSFT]

Thanks for the proposal, @NinoFloris.
It looks great. We'll mark this as help-wanted so community members can handle this too.

[mareklinka]

Hello all. This looks rather straight-forward - if it's still open, I'd like to take a crack at it. Is there anything special or important that I should be aware of?