fix: guard OSArchitecture access against PropertyNotFoundException under strict mode

[Copilot]

On Windows PowerShell 5.1 with older .NET Framework, [System.Runtime.InteropServices.RuntimeInformation]::OSArchitecture can throw PropertyNotFoundException under Set-StrictMode -Version Latest, intermittently blocking SDK bootstrap.

Changes

• scripts/get-dotnetup.ps1: Wrap RuntimeInformation::OSArchitecture access in a standalone helper patterned after the SDK toolset scripts' existing native-architecture helper. On failure, the helper falls back to the same default behavior used by those scripts.

This keeps get-dotnetup.ps1 standalone while aligning its architecture detection behavior with the existing SDK toolset helpers.

It also adds a test to keep the two implementations in sync since main cannot have the script and the script must work standalone.

[Copilot]

Pull request overview

This PR hardens get-dotnetup.ps1 runtime architecture detection to avoid PropertyNotFoundException from [RuntimeInformation]::OSArchitecture when running under Windows PowerShell 5.1 with Set-StrictMode -Version Latest, preventing bootstrap failures on older .NET Framework environments.

Changes:

• Wraps RuntimeInformation::OSArchitecture access in try/catch and falls back when it fails.
• Adds fallback architecture detection via $env:PROCESSOR_ARCHITECTURE on Windows and uname -m on Linux/macOS.

[dsplaisted]

@nagilson Is this still valid? Was it fixed when flowing the scripts to main or elsewhere?

[nagilson]

It's not fixed yet, I'm waiting for #54756 to merge now and maybe merge with main again after that. I need to clean up the AI code.

[nagilson]

A great test for this is to use sandbox, because that defaults to Windows Powershell with a framework version that fails to load the Runtime Architecture APIs.

I was able to confirm that the script now works properly.

[nagilson]

the failing test is flakey and this def did not cause a nuget breaking change