Add System.Collections.Concurrent.ConcurrentHashSet<T>

### Background and motivation

Basically reopening issue #39919.

I'm pretty sure that even a simple wrapper around `ConcurrentDictionary` would be useful. There must be many codebases out there that either implement their own `ConcurrentHashSet` or use `ConcurrentDictionary` as a workaround.

### API Proposal

#39919

### API Usage

#39919

### Alternative Designs

_No response_

### Risks

_No response_

Start by reading the referenced issue #39919 and comparing its API proposal and usage with the existing ConcurrentDictionary workaround. This issue is complete when the ConcurrentHashSet API has an agreed design and the proposed collection is added to System.Collections.Concurrent.

Written by the indexing model from the issue text.