Add FileTracker package consumption specification

[Copilot]

Context

FileTracker binaries (Tracker.exe, FileTracker32.dll, FileTracker64.dll, FileTrackerA4.dll) are closed-source but distributed with MSBuild. Currently sourced from VS installations during bootstrap, making coordinated changes and testing difficult without VS installed.

Issue #649 requested package-based distribution but was closed as "not_planned" per maintainer: "This doesn't seem that important at the moment."

Changes Made

• Added documentation/specs/proposed/filetracker-package-consumption.md documenting:
  • Current implementation (VS-sourced binaries in bootstrap, runtime loading via InprocTrackingNativeMethods.cs)
  • Proposed two-phase solution: internal package creation + MSBuild repo consumption
  • Required changes to eng/Versions.props, Directory.Packages.props, eng/BootStrapMsBuild.targets
  • Test infrastructure updates needed
  • Why this was deferred

Testing

Documentation-only change. No code changes to test.

Notes

Full implementation requires Microsoft internal work to create the Microsoft.Build.FileTracker package from closed-source binaries. This spec provides the roadmap for MSBuild repo changes when/if prioritized.

Original prompt

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This section details on the original issue you should resolve

<issue_title>FileTracker should be consumed from a package</issue_title>
<issue_description>The source code for Tracker.exe and FileTracker.dll is not open source, but those assemblies are part of the MSBuild binary distribution. We should build them internally and make them available as a package so that the built-from-GitHub version of MSBuild can include them and ship them back into Visual Studio (or other consumers). Currently tests fall back to the installed versions, which makes testing coordinated changes very difficult.
</issue_description>

<agent_instructions>please fix this issue on the top of the changes from #13094</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@rainersigwald This doesn't seem that important at the moment.

• Fixes FileTracker should be consumed from a package #649

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[dotnet-policy-service]

Hello @@copilot, I noticed that you’re changing an .swr file or any file under src/Package/MSBuild.VSSetup.. Please make sure to validate this change by an experimental VS insertion. This is accomplished by pushing to an exp/* branch, which requires write permissions to this repo.