Enable polyglot feature flag in E2E CLI tests

[Copilot]

Description

Polyglot E2E tests (Python, TypeScript/React) require the features:polyglotSupportEnabled flag to access polyglot templates and commands. Without this flag, CLI commands like aspire init -l python fail as the feature is gated.

Changes:

• Extended SourceAspireCliEnvironment() with optional enablePolyglotSupport parameter
• Sets features__polyglotSupportEnabled=true environment variable when enabled
• Supports both PowerShell (Windows) and Bash (Linux/macOS) syntax
• Enabled flag in polyglot test classes:
  • PolyglotPythonTests - Python AppHost with Redis
  • PythonReactTemplateTests - FastAPI/React template
  • JsReactTemplateTests - ASP.NET Core/React (TypeScript) template

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
  • No
• Does the change require an update in our Aspire docs?
  • Yes
  • No

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[sebastienros]

@mitchdenny this used Sonnet 4.5 and my local attempts using Opus ended up with the simplest solution which seems correct ... currently testing.