Perf issue: http.sys doesn't share ConnectionInfo class between requests of the same connection

It might be to simplify the design (and might be infeasible to do some other way) but for http.sys (ie webserver still used by _many_ big internal services) `ConnectionInfo` as well as ` ITlsConnectionFeature` interface is tied to the instance of `RequestContext` which means there's new instance per each requests. Ie new instances for even requests on the same connection.

That by itself isn't an issue, but the way `Task ITlsConnectionFeature.GetClientCertificateAsync(CancellationToken cancellationToken)` works is that it tries to cache the cert on the underlying instance, which in this case is new one per each requests.

This means that code that tries to validate MTLS (very common at microsoft, and with new protocols won't be entirely going away even with HPA work (plans to be used _with_ other protocols)) per each request (which is common by internal auth libraries) allocates the whole _not small_ cert per each requests. When it'd be more than enough to do it per each connection.

For our service this ends up being > few percent of _all allocations_. And since these survive the whole requests' lifetime, they'll be bad allocs that live longer. Across whole MS it'll be a lot of memory pressure wasted.