Prepare version 4.2.0 release

[Copilot]

Prepares the repository for the 4.2.0 release by updating the changelog with release notes and bumping version numbers in the build configuration.

Changes

• Changelog: Added version 4.2.0 entry at the top of changelog.md documenting new features, bug fixes, dependency updates, and test improvements
• New features: CAE claims support for FIC + Managed Identity, AddMicrosoftIdentityMessageHandler extension methods for IHttpClientBuilder
• Bug fixes: Tenant propagation in credential FIC acquisition, ForAgentIdentity configuration section handling, GetTokenAcquirer options propagation, identity configuration error messaging
• Dependencies: Microsoft.Identity.Abstractions 9.6.0→10.0.0, express 5.1.0→5.2.0, jws 3.2.2→3.2.3
• Fundamentals: Support policy update, E2E test configuration updates for agent identity
• Version Updates: Updated MicrosoftIdentityWebVersion from 4.1.1 to 4.2.0 and MicrosoftIdentityAbstractionsVersion from 9.6.0 to 10.0.0 in Directory.Build.props

The changelog entry follows the existing format and structure, positioned before the 4.1.1 release notes. All version numbers and dependencies are now aligned for the 4.2.0 release.

Original prompt

Update changelog for version 4.2.0

Update the changelog.md file to include the release notes for version 4.2.0 (not 4.1.2, as this includes public API changes).

Add the following entry at the very top of the changelog, before the existing ## 4.1.1 section:

## 4.2.0

### New features
- **Added CAE claims support for FIC + Managed Identity**. See [#3647](https://github.com/AzureAD/microsoft-identity-web/pull/3647) for details.
- **Added `AddMicrosoftIdentityMessageHandler` extension methods for `IHttpClientBuilder`**. See [#3649](https://github.com/AzureAD/microsoft-identity-web/pull/3649) for details.

### Bug fixes
- **Fixed tenant not being propagated in credential FIC acquisition**. See [#3633](https://github.com/AzureAD/microsoft-identity-web/pull/3633) for details.
- **Fixed `ForAgentIdentity` hardcoded 'AzureAd' `ConfigurationSection` to respect `AuthenticationOptionsName`**. See [#3635](https://github.com/AzureAD/microsoft-identity-web/pull/3635) for details.
- **Fixed `GetTokenAcquirer` to propagate `MicrosoftEntraApplicationOptions` properties**. See [#3651](https://github.com/AzureAD/microsoft-identity-web/pull/3651) for details.
- **Added meaningful error message when identity configuration is missing**. See [#3637](https://github.com/AzureAD/microsoft-identity-web/pull/3637) for details.

### Dependencies updates
- Bump express from 5.1.0 to 5.2.0 in /tests/DevApps/SidecarAdapter/typescript. [#3636](https://github.com/AzureAD/microsoft-identity-web/pull/3636)
- Bump jws from 3.2.2 to 3.2.3 in /tests/DevApps/SidecarAdapter/typescript. [#3641](https://github.com/AzureAD/microsoft-identity-web/pull/3641)

### Fundamentals
- Update agent identity coordinates in E2E tests after deauth. [#3640](https://github.com/AzureAD/microsoft-identity-web/pull/3640)
- Update E2E agent identity configuration to new tenant. [#3646](https://github.com/AzureAD/microsoft-identity-web/pull/3646)

Ensure the formatting and structure match the existing changelog entries.

This pull request was created from Copilot chat.

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[jmprieur]

@copilot. Let's also update in the Directory.Build.props file:

• the MicrosoftIdentityAbstractionsVersion to 10.0.0
• the default value for MicrosoftIdentityWeb to 4.2.0

and let's add the change on the Microsoft.Identity.Web.Abstractions dependency in the release notes.

This way, we'll then be ready for the release in one PR!

[Copilot]

@copilot. Let's also update in the Directory.Build.props file:

• the MicrosoftIdentityAbstractionsVersion to 10.0.0
• the default value for MicrosoftIdentityWeb to 4.2.0
  ...

Done! Updated:

• MicrosoftIdentityWebVersion to 4.2.0
• MicrosoftIdentityAbstractionsVersion to 10.0.0
• Added Microsoft.Identity.Abstractions dependency update to the changelog

Commit: 01b664b

[jmprieur]

@copilot, I see that @bgavrilMS merged this PR without notice: #3656
do you mind adding it to fundamental section as well ....

[Copilot]

@copilot, I see that @bgavrilMS merged this PR without notice: #3656
do you mind adding it to fundamental section as well ....

Added support policy update (PR #3656) to the Fundamentals section.

Commit: b63e9ba

[jmprieur]

LGTM
Thanks