AoT - Part 3 - Upgrade to Abstractions 11 that are AoT compatible

[jmprieur]

{PR title}

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Summary of the changes (Less than 80 chars)

Description

{Detail}

Fixes #{bug number} (in this specific format)

[Copilot]

Pull request overview

Upgrades the repo to Microsoft.Identity.Abstractions v11 and adjusts related code paths to remain compatible with AoT and newer TFMs (including net10), alongside moving the solution to C# 14.

Changes:

• Bump MicrosoftIdentityAbstractionsVersion to 11.0.0 and set LangVersion to 14.
• Update logging helpers (block-bodied methods + nullable thumbprint logging) and record the internal API delta in InternalAPI.Unshipped.txt.
• Adjust certificate handling for net10 via conditional compilation in CertificateDescription.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/Microsoft.Identity.Web.Test/CertificatesObserverTests.cs	Tweaks test handler thumbprint comparison to tolerate nulls.
src/Microsoft.Identity.Web.TokenAcquisition/TokenAcquisition.Logger.cs	Converts logger wrappers to block-bodied methods (AoT-friendly pattern).
src/Microsoft.Identity.Web.TokenAcquisition/PublicAPI/*/InternalAPI.Unshipped.txt	Records new internal API signature for nullable cert thumbprint logging across TFMs.
src/Microsoft.Identity.Web.TokenAcquisition/ConfidentialClientApplicationBuilderExtension.cs	Passes nullable thumbprint into logging call when selecting certificate credentials.
src/Microsoft.Identity.Web.TokenAcquisition/ConfidentialClientApplicationBuilderExtension.Logger.cs	Updates logger wrappers and makes UsingCertThumbprint accept nullable thumbprints.
src/Microsoft.Identity.Web.Certificate/CertificateDescription.cs	Conditionalizes Certificate property implementation for NET10_0_OR_GREATER.
Directory.Build.props	Moves to C# 14 and upgrades Abstractions dependency version.