Unify certificate validation code on OSX between SslStream and QuicConnection

[rzikm]

Follow-up on #117472, now that we have managed implementation of X509 name check, we can get rid of the code which was originally bound to SslContext. This PR unifies certificate validation code between SslStream and QuicConnection.

[Copilot]

Pull Request Overview

This PR removes the legacy macOS-specific hostname‐matching code paths and redirects certificate validation on OSX to the shared BuildChainAndVerifyProperties logic.

• Removes AppleCryptoNative_SslIsHostnameMatch implementation and related P/Invoke/entrypoint.
• Refactors CertificateValidationPal.OSX.VerifyCertificateProperties to call the unified validator.
• Adds common validation helper file and updates the project to include it.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/native/libs/System.Security.Cryptography.Native.Apple/pal_ssl.h	Dropped the old hostname-matching export.
src/native/libs/System.Security.Cryptography.Native.Apple/pal_ssl.c	Removed the entire SslIsHostnameMatch implementation.
src/native/libs/System.Security.Cryptography.Native.Apple/entrypoints.c	Deleted the DllImport entry for hostname matching.
src/libraries/System.Net.Security/src/System/Net/CertificateValidationPal.OSX.cs	Replaced platform code with call to BuildChainAndVerifyProperties.
src/libraries/System.Net.Security/src/System.Net.Security.csproj	Added new common validation source for OSX.
src/libraries/Common/src/Interop/OSX/System.Security.Cryptography.Native.Apple/Interop.Ssl.cs	Removed IDN mapping and hostname-check P/Invoke shim.

Comments suppressed due to low confidence (2)

src/libraries/System.Net.Security/src/System/Net/CertificateValidationPal.OSX.cs:8

• [nitpick] Consider using a file-scoped namespace declaration (e.g., namespace System.Net;) to align with project conventions and reduce indentation.

namespace System.Net

src/libraries/System.Net.Security/src/System/Net/CertificateValidationPal.OSX.cs:20

• Add unit tests covering the unified certificate validation logic on macOS—particularly hostname matching and chain validation—to verify parity with the previous implementation.

            return CertificateValidation.BuildChainAndVerifyProperties(chain, remoteCertificate, checkCertName, isServer, hostName, Span<byte>.Empty);

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[liveans]

Seems like this is affecting some test cases: OSX Tests

[liveans]

LGTM. I think this will simplify changes we made in NW PR?

[wfurt]

nice. lot of deletes. I hope the more code works properly :)

[rzikm]

/ba-g infrastructure faliures are unrelated