RDKEMW-6167: Update Display Settings with libds client library

[Dosakaya]

Reason for change: Update Display Settings with libds client library.
Test Procedure: test all end-to-end tests for all new events

Risks: NO
Priority: P1

[CLAassistant]

All committers have signed the CLA.

[skamath]

A common observation, in all event notification callbacks, I see there is a check for being valid DisplaySettings::_instance. We should really try and understand what use case will we hit the issue, and please document the usecase.

[skamath]

I don't see deletion of old static methods (originally receiving notification over IARM).
Also make sure dsMgr.h and other unused headers are no more included.

[Copilot]

Pull Request Overview

This PR migrates the DisplaySettings plugin from IARM-based event handling to a device library-based event handling system. The change replaces legacy IARM event registration and handlers with modern C++ interface implementations for better type safety and maintainability.

Key changes:

• Replaces IARM event handlers with device library interface implementations
• Adds multiple interface inheritance for handling different types of display and audio events
• Refactors initialization and deinitialization logic to use device::Manager instead of IARM

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
DisplaySettings.h	Adds interface inheritance and declares new event handler methods while removing IARM function declarations
DisplaySettings.cpp	Implements new device library event handlers and removes IARM-based event handling code

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