Implement support for loading multiple providers into a single context

[vcsjones]

Closes #113118

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[Copilot]

Pull request overview

This PR extends the OpenSSL provider key-loading path to support loading multiple OpenSSL 3 providers into a single OSSL_LIB_CTX, and exposes a new managed overload that accepts a provider list plus an optional OpenSSL property query passed to OSSL_STORE_open_ex.

Changes:

• Add SafeEvpPKeyHandle.OpenKeyFromProvider(IEnumerable<string> providerNames, string keyUri, string? propertyQuery = null) and update the native interop to accept multiple provider names.
• Update native provider loading to load all requested providers into one library context and pass propertyQuery through to OSSL_STORE_open_ex.
• Expand manual tests to cover new overload argument validation and property query scenarios.

Show a summary per file

File	Description
src/native/libs/System.Security.Cryptography.Native/pal_evp_pkey.h	Update native API contract to accept multiple providers + property query.
src/native/libs/System.Security.Cryptography.Native/pal_evp_pkey.c	Implement multi-provider loading/unload-on-partial-failure; pass property query to OSSL_STORE_open_ex.
src/libraries/Common/src/Interop/Unix/System.Security.Cryptography.Native/Interop.EvpPkey.cs	Update P/Invoke signature and managed interop wrapper for the new native contract.
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/SafeEvpPKeyHandle.OpenSsl.cs	Add new public overload, argument validation, provider-set caching keying, and wire to updated interop.
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/OpenSsl.NotSupported.cs	Add the new overload stub for unsupported platforms.
src/libraries/System.Security.Cryptography/ref/System.Security.Cryptography.cs	Add the new public API surface to the reference assembly.
src/libraries/System.Security.Cryptography/src/Resources/Strings.resx	Add a new resource string for empty-collection validation.
src/libraries/System.Security.Cryptography/tests/OpenSslNamedKeysTests.manual.cs	Add/adjust manual tests for the new overload and property query behavior.

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 3

[Copilot]

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 2

[Copilot]

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 2

[Copilot]

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 2

[Copilot]

Copilot's findings

• Files reviewed: 8/8 changed files
• Comments generated: 0 new