[minor][Feature]: Support POP and claims in browser core

[antrix1989]

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Proposed changes

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Type of change

• Feature work
• Bug fix
• Documentation
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Additional information

[Copilot]

Pull request overview

Adds support in the browser native message “GetToken” request parsing for PoP authentication scheme parameters and claims, with accompanying unit tests.

Changes:

• Parse tokenType + reqCnf from the browser native message request and construct MSIDAuthenticationSchemePop (fallback to Bearer).
• Parse claims from the request and build an MSIDClaimsRequest.
• Add unit tests covering claims parsing and PoP/Bearer scheme selection.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
IdentityCore/src/broker_operation/request/browser_native_message_request/MSIDBrowserNativeMessageGetTokenRequest.m	Adds parsing/initialization for PoP auth scheme and claims request.
IdentityCore/src/broker_operation/request/browser_native_message_request/MSIDBrowserNativeMessageGetTokenRequest.h	Exposes new authScheme and claimsRequest properties on the request model.
IdentityCore/tests/MSIDBrowserNativeMessageGetTokenRequestTests.m	Adds coverage for claims parsing and PoP/Bearer scheme behavior.

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[kaisong1990]

@antrix1989 Approved with some comments