Update files for Microsoft Identity Web 4.0.0 release

[Copilot]

This PR updates the necessary files to prepare for the Microsoft Identity Web 4.0.0 release, addressing the version configuration, changelog requirements, and API compatibility baselines.

Changes Made

1. Updated changelog.md

Added 4.0.0 release notes at the top of the file with:

• Breaking Changes: Removal of .NET 6.0 and .NET 7.0 support following Microsoft's support lifecycle
• New Features: Various improvements to performance logging, authentication, and credential loading capabilities
• Fundamentals: Various improvements to .NET support and dependency optimizations

2. Updated Directory.Build.props

• Updated MicrosoftIdentityWebVersion from 3.14.1 to 4.0.0
• Updated PackageValidationBaselineVersion from 2.7.0 to 3.14.1

3. Generated API Compatibility Baseline Files

• Ran dotnet pack Microsoft.Identity.Web.sln /p:GenerateCompatibilitySuppressionFile=true
• Generated/updated CompatibilitySuppressions.xml files for all projects
• Created baseline API compatibility files for package validation

Key Highlights

The 4.0.0 release introduces significant breaking changes by removing support for both .NET 6.0 and .NET 7.0, aligning with Microsoft's support lifecycle. The supported target frameworks are now:

• .NET 8.0
• .NET 9.0
• .NET Framework 4.6.2
• .NET Framework 4.7.2
• .NET Standard 2.0

The release also includes various improvements to performance logging, authentication, and dependency optimizations.

Validation

• ✅ Build system correctly picks up the new version 4.0.0
• ✅ Project builds and packs successfully with the updated configuration
• ✅ API compatibility baseline files generated successfully
• ✅ All review feedback addressed by removing references to unmerged PRs
• ✅ Breaking changes updated to include both .NET 6.0 and .NET 7.0 removal

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Files to Update for 4.0.0 Release</issue_title>
<issue_description>1. changelog.md - Add this at the very top (line 1):

4.0.0
=========
### Breaking Changes
**Removed support for .NET 6.0** - Microsoft Identity Web 4.0.0 no longer targets .NET 6.0, following Microsoft's support lifecycle. The supported target frameworks are now .NET 8.0, .NET 9.0, .NET Framework 4.6.2, .NET Framework 4.7.2, and .NET Standard 2.0.

### New features
- Enhanced performance logging in credential providers. See PR [#3495](https://github.com/AzureAD/microsoft-identity-web/pull/3495) for details.
- Improved certificateless authentication documentation and developer experience. See PR [#3494](https://github.com/AzureAD/microsoft-identity-web/pull/3494) for details.
- Enhanced SigningCredential loading capabilities in DefaultCredentialsLoader. See PR [#3361](https://github.com/AzureAD/microsoft-identity-web/pull/3361) for details.

### Fundamentals
- Updated containerization support for modern .NET versions. See PR [#3481](https://github.com/AzureAD/microsoft-identity-web/pull/3481) for details.
- Improved .NET 10 Preview support preparations. See PR [#3449](https://github.com/AzureAD/microsoft-identity-web/pull/3449) for details.
- Enhanced dependency cleanup and optimization. See PR [#3314](https://github.com/AzureAD/microsoft-identity-web/pull/3314) for details.

2. Directory.Build.props - Update these two lines:
   Line 5: Change:

<MicrosoftIdentityWebVersion Condition="'$(MicrosoftIdentityWebVersion)' == ''">3.14.1</MicrosoftIdentityWebVersion>

To:

<MicrosoftIdentityWebVersion Condition="'$(MicrosoftIdentityWebVersion)' == ''">4.0.0</MicrosoftIdentityWebVersion>

Line 10: Change:

<PackageValidationBaselineVersion>2.7.0</PackageValidationBaselineVersion>

to:

<PackageValidationBaselineVersion>3.14.1</PackageValidationBaselineVersion>

Thank you!
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #3497

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[jmprieur]

Thanks @jennyf19
don't we need to run

dotnet pack Microsoft.Identity.Web.sln /p:GenerateCompatibilitySuppressionFile=true

[jennyf19]

@copilot can you run dotnet pack Microsoft.Identity.Web.sln /p:GenerateCompatibilitySuppressionFile=true and create the baseline API files?

[Copilot]

@copilot can you run dotnet pack Microsoft.Identity.Web.sln /p:GenerateCompatibilitySuppressionFile=true and create the baseline API files?

Successfully ran the dotnet pack command and generated the API compatibility baseline files in commit 449f28d.

[keegan-caruso]

few small comments