CngProperty constructor with ReadOnlySpan<byte> overload

[krwq]

Fixes: #69061

This is written by copilot based on #93805 + review and feedback to agent

[Copilot]

Pull request overview

Adds a public CngProperty constructor overload that accepts ReadOnlySpan<byte> to avoid forcing callers to materialize a byte[] before constructing the property, aligning with the API proposal in #69061.

Changes:

• Exposed a new public CngProperty(string, ReadOnlySpan<byte>, CngPropertyOptions) constructor and documented it.
• Updated the reference assembly to include the new constructor signature.
• Added tests validating behavioral equivalence between the byte[] and ReadOnlySpan<byte> constructor paths (including empty/default span cases and CNG roundtrips).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/CngProperty.cs	Makes the span-based constructor public, adds XML docs, and defensively copies the span via ToArray().
src/libraries/System.Security.Cryptography/ref/System.Security.Cryptography.cs	Adds the new constructor to the ref surface area.
src/libraries/System.Security.Cryptography.Cng/tests/PropertyTests.cs	Adds coverage ensuring span ctor matches array ctor semantics for equality, GetValue(), and key property set/get behavior.