[10.0.1xx] Use dotnetup preview for SDK acquisition

[nagilson]

Please see #55640

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[Copilot]

Pull request overview

Backports the “use dotnetup preview for acquisition” work to the 10.0.1xx servicing branch, updating toolset bootstrap and test-runtime acquisition to prefer dotnetup (with fallbacks) and to better support cross-architecture Helix payloads.

Changes:

• Add shared dotnetup acquisition helpers (bash/PowerShell) and repo-owned architecture helpers used by build/test scripts.
• Update toolset restore/configure scripts to install SDKs and test runtimes via dotnetup, including cross-build sidecar runtime handling and an MSBuild overlay step for Helix payloads.
• Adjust a publish test to dynamically discover the installed 8.0.x runtime folder when dotnetup only installs latest patches.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/Microsoft.NET.Publish.Tests/GivenThatAPublishedDepsJsonShouldContainVersionInformation.cs	Dynamically selects an installed 8.0.x runtime version for --fx-version execution.
src/Layout/redist/targets/OverlaySdkOnLKG.targets	Adds target to overlay cross-arch test runtimes into the Helix test host from an artifacts sidecar.
eng/sdk-tools.sh	Adds repo-owned bash helper for native machine architecture detection (incl. Rosetta handling).
eng/sdk-tools.ps1	Adds repo-owned PowerShell helpers for native/process architecture detection.
eng/restore-toolset.sh	Switches test runtime acquisition to dotnetup with cross-arch sidecar behavior and install-script fallback.
eng/restore-toolset.ps1	Switches test runtime acquisition to dotnetup with cross-arch sidecar behavior and install-script fallback.
eng/dotnetup-shared.sh	Adds shared bash helpers for dotnetup caching, acquisition, and non-errexit command execution.
eng/dotnetup-shared.ps1	Adds shared PowerShell helpers for dotnetup caching, acquisition, and safe native invocation.
eng/configure-toolset.sh	Pre-installs bootstrap SDK(s) from global.json using dotnetup into repo-local .dotnet.
eng/configure-toolset.ps1	Pre-installs bootstrap SDK(s) from global.json using dotnetup into repo-local .dotnet.
.gitignore	Ignores dotnetup build output under eng/dotnetup/.

Suppressed comments (1)

eng/restore-toolset.ps1:100

• The generated sdk-build-env.ps1 no longer sets DOTNET_MULTILEVEL_LOOKUP=0. This repo disables multi-level lookup for deterministic builds (see eng/common/tools.ps1:160-162), and the generated script is meant to be executed in a fresh PowerShell session.

    $scriptContents = @"
`$host.ui.RawUI.WindowTitle = "SDK Build ($RepoRoot)"
# https://aka.ms/vs/unsigned-dotnet-debugger-lib
`$env:VSDebugger_ValidateDotnetDebugLibSignatures=0

`$env:DOTNET_ROOT="$env:DOTNET_INSTALL_DIR"
`$env:DOTNET_MSBUILD_SDK_RESOLVER_CLI_DIR="$env:DOTNET_INSTALL_DIR"

[nagilson]

/azp run

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