Limit ITlsHandshakeFeature.Exception on Connections.Abstractions for #if NETCOREAPP

[DeagleGross]

#65807 introduced Exception property with #if NET_11_OR_GREATER which makes release of Connections.Abstractions be TFM dependant as well. We should make the APIs match across different TFMs for same NuGet version.

I think simply returning null is ok here. I do not like the idea of throwing an exception as DIM, because that's an extra thing for the user to handle. For net10 apps referncing net11 NuGet package it will throw everytime, which is impacting perf for no reason

[Copilot]

Pull request overview

Aligns the ITlsHandshakeFeature.Exception API surface across the Connections.Abstractions netcoreapp TFMs (e.g., net10 and net11) for the same package version by gating it on NETCOREAPP and providing a default null implementation.

Changes:

• Switch ITlsHandshakeFeature.Exception compilation guard from NET11_0_OR_GREATER to NETCOREAPP.
• Add the Exception getter to the net10 public API unshipped list.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Servers/Connections.Abstractions/src/PublicAPI/net10.0/PublicAPI.Unshipped.txt	Declares the new ITlsHandshakeFeature.Exception getter as part of the net10 API surface.
src/Servers/Connections.Abstractions/src/Features/ITlsHandshakeFeature.cs	Makes Exception available for all NETCOREAPP builds with a default null implementation.

[halter73]

I think simply returning null is ok here. I do not like the idea of throwing an exception as DIM, because that's an extra thing for the user to handle. For net10 apps referncing net11 NuGet package it will throw everytime, which is impacting perf for no reason

Agreed. Did you test out the preview package/dll with the net10 ASP.NET Core shared framework? I totally understand if you didn't. But if not, try to do this after this gets released as a preview at least.