Add build.ps1 for multi-Roslyn Build/Test/Pack orchestration

[atifaziz]

Objective

Create a repository-root build.ps1 script with parameter sets to standardize Build, Test, and Pack workflows across Roslyn variants.

Scope

• Implement Build (default), Test, and Pack parameter sets.
• Ensure script is directory-independent (Push-Location $PSScriptRoot / Pop-Location in finally).
• Use strict error handling and propagate non-zero exit codes.

Files

• build.ps1

Tasks

• Create parameter sets:
  • Build (default) with -Configuration (default Release)
  • Test with -Configuration and -NoBuild
  • Pack with -Configuration and optional -VersionSuffix
• Add Build flow:
  • Run dotnet build solution baseline.
  • Run dotnet build src/DocoptNet/DocoptNet.csproj -f netstandard2.0 -p:RoslynVersion=4.4.
• Add Test flow:
  • Optionally run Build flow when -NoBuild is not set.
  • Run baseline tests with dotnet test --no-build when applicable.
  • Run Roslyn 4.4 tests via test project with -p:RoslynVersion=4.4.
• Add Pack flow:
  • Always invoke Build flow first.
  • Run dotnet pack src/DocoptNet/DocoptNet.csproj --no-build.
  • Pass --version-suffix only when provided.
• Enforce $ErrorActionPreference = 'Stop' and fail fast on $LASTEXITCODE.

Acceptance Criteria

• dotnet pwsh ./build.ps1 completes baseline + Roslyn 4.4 build.
• dotnet pwsh ./build.ps1 -Test runs test pass for both variants.
• dotnet pwsh ./build.ps1 -Pack succeeds and returns non-zero on failures.
• Script works from any current working directory.

Dependencies

• Depends on Issue Add RoslynVersion configuration in project #207 for Roslyn property and pack guard behavior.

Notes

• Assume dotnet tool restore has already been run so dotnet pwsh is available.