Target pwsh LTS .NET Framework

[jshigetomi]

PR Summary

This pull request updates the build system and project configuration for PSReadLine to target .NET 8.0, simplifies the build process by removing polyfill support, and updates dependencies accordingly. The changes ensure the build dynamically determines the target framework, and streamline the layout and test tasks to match the new structure.

Build and Target Framework Modernization:

• The PSReadLine project now targets .NET 8.0 instead of .NET Standard 2.0, as specified in PSReadLine.csproj. The build script (PSReadLine.build.ps1) dynamically reads the target framework from the project file, removing the need for manual selection or validation of frameworks. [1] [2]
• A new global.json file pins the .NET SDK version to 8.0.416 to ensure consistent builds across environments.

Simplification and Cleanup:

• All references to the Polyfill project and related build steps have been removed from the build script and project file, streamlining the build and layout process. [1] [2] [3] [4]
• Dependency management has been updated: PowerShellStandard.Library and the Polyfill project reference were removed, and Microsoft.PowerShell.SDK was added as a new package dependency.

Build Script Adjustments:

• The build, test, and layout tasks in PSReadLine.build.ps1 now use the dynamically determined target framework, improving maintainability and reducing manual errors. [1] [2] [3] [4]

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure you've added one or more new tests
• Make sure you've tested these changes in terminals that PowerShell is commonly used in (i.e. conhost.exe, Windows Terminal, Visual Studio Code Integrated Terminal, etc.)
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed at PowerShell-Docs
    • Doc Issue filed: