Add PwshHandler for native PowerShell 7.0+ Tasks

[MJECloud]

Context

This PR adds support for a new Pwsh task execution handler so tasks can explicitly run with PowerShell 7+ (pwsh) on Windows, Linux, and macOS.

The motivation is to build tasks for AzureDevOps which can be pure written in PowerShell like PowerShell3 and PowerShellExeHandler - No Typescript/Node needed.

Closes #4386

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Description

Introduces a new Pwsh execution entry in task execution data and wires it through handler selection, handler creation, and execution.

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Risk Assessment (Low)

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Unit Tests Added or Updated (Yes)

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Additional Testing Performed

• Real pipeline validation on Windows using a patched self-hosted agent
• Real pipeline validation on Ubuntu using a patched self-hosted agent
• Successful execution of a simple Pwsh smoke task
• Successful execution of a richer task using a modificated bundled VstsTaskSdk (Also created a PR for that)
• Failure-path validation when pwsh is missing, verifying that the task fails explicitly

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Change Behind Feature Flag (No)

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Tech Design / Approach

• Keeps Pwsh compatible with existing PowerShell task packaging (VstsTaskSdk + target)
• Adds a separate cross-platform handler instead of extending legacy Windows-only handlers
• Resolves pwsh at execution time, not at agent startup
• Supports container step hosts through the modern handler execution path
• Does not fall back to Windows PowerShell, so Pwsh stays explicit and predictable

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Documentation Changes Required (No)

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Logging Added/Updated (Yes)

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Telemetry Added/Updated (No)

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Rollback Scenario and Process (No)

It's not breaking any working functionality

Dependency Impact Assessed and Regression Tested (Yes)

• All impacted internal modules, APIs, services, and third-party libraries are analyzed.
• Results are reviewed and confirmed to not break existing functionality.

[azure-pipelines]

Azure Pipelines:
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[MJECloud]

@geekzter any chance that someone can look into that? 😊
Thank you in advance!

[azure-pipelines]

Azure Pipelines:
1 pipeline(s) require an authorized user to comment /azp run to run.

[azure-pipelines]

Azure Pipelines:
1 pipeline(s) require an authorized user to comment /azp run to run.