[vs15.9] Merge tag v15.9.30

[surayya-MS]

Fixes #

Context

Changes Made

Testing

Notes

[Copilot]

Pull Request Overview

This PR merges tag v15.9.30 and modernizes several areas including async file download logic, package feeds, signing configuration, and CI pipelines.

• Refactored DownloadFile task to async with proper cancellation, retry, and logging
• Updated package feeds, signing certificates, and build scripts to newer URLs and tooling
• Migrated Azure Pipelines definitions to the 1ES MicroBuild template and updated VM images

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Tasks/DownloadFile.cs	Converted synchronous download to async/await, improved cancellation and retry logic
src/MSBuildTaskHost/MSBuildTaskHost.csproj	Disabled PdbGit package reference temporarily
src/Build.UnitTests/BackEnd/TaskRegistry_Tests.cs	Removed unused using
setup/Microsoft.Build.swixproj	Switched Authenticode from Vsix to Microsoft400
global.json	Bumped RoslynTools.RepoToolset to 1.1.0-beta3.21064.1
build/build.ps1	Initialized LASTEXITCODE before dotnet install
build/Versions.props	Consolidated restore sources into Azure feeds
build/SignToolData.json	Updated certificate name to Microsoft400
build/SetMicrobuildVersion/SetMicrobuildVersion.csproj	Adopted Sdk style project and added TargetFramework
NuGet.Config	Updated roslyn-tools feed URL
Directory.Build.props	Overrode dead feed with active Azure feeds
.vsts-dotnet.yml	Switched to MicroBuild 1ES template with variables and resources
.vsts-dotnet-ci.yml	Updated VM images and VS command paths to current versions

Comments suppressed due to low confidence (2)

src/Tasks/DownloadFile.cs:77

• The new async execution path (ExecuteAsync) and cancellation/retry behaviors aren’t covered by existing unit tests. Add tests to verify correct cancellation handling and retry logic.

private async Task<bool> ExecuteAsync()

src/Tasks/DownloadFile.cs:282

• Removing the Content-Disposition header fallback loses the ability to name files based on server headers. Reintroduce response.Content.Headers.ContentDisposition?.FileName as an intermediate fallback before using the URI path.

: Path.GetFileName(requestUri.LocalPath); // Otherwise attempt to get a file name from the URI