Add new additionalPowerShellLocations option

[chawyehsu]

PR Summary

Implement and close #5233

This PR attempts to add a better (cross-platform friendly) way to configure additional PowerShell paths.

Details

This implementaion is a little different from what I've proposed last year in #5233, the primary difference is instead of a default?: boolean field, a weight?: number is used to rank entries and select the best matching entry. Since we cannot restrict the default: true per platform to only one in the VS Code extension configuration, using weighted sorting allows us to achieve a similar purpose. Furthermore, the more specific platform field involving arch is used to specify the target host instead of os.

Backward Compatibility? Yes

While the old powerShellAdditionalExePaths and powerShellDefaultVersion stay unchanged and can still be used to define additional PowerShell paths, the new additionalPowerShellLocations is added to be mutually exclusive, which means when additionalPowerShellLocations is defined(non-empty), old options are ignored. This keeps settings non-conflicting: users pick one path (old or new), not both. Intuitive, simple and easy to understand.

Old options could be marked deprecated after a transition period.

PR Checklist

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[Copilot]

Pull request overview

Adds a new cross-platform-friendly configuration option (powershell.additionalPowerShellLocations) to let users define additional PowerShell executables with per-platform (OS+arch) filtering and weighted ranking, integrating it into PowerShell discovery and the Session Menu flow.

Changes:

• Added SupportedPlatform, IAdditionalPowerShellLocation, and getSupportedPlatform() plus a new enumeration path for additional locations in PowerShellExeFinder.
• Updated SessionManager to prefer additionalPowerShellLocations over legacy settings and to adjust entry weight when switching via Session Menu.
• Added unit tests for supported-platform mapping and additional-location filtering/sorting; added the new setting schema to package.json.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/platform.ts	Introduces the new platform/arch mapping + additional-location enumeration and integrates it into PowerShell discovery.
src/session.ts	Reads the new setting, uses it to derive the requested PowerShell, and updates weight on Session Menu selection.
test/core/platform.test.ts	Adds coverage for platform mapping and additional-location filtering/priority behavior.
package.json	Adds powershell.additionalPowerShellLocations configuration schema and documentation.