Refactor CI artifacts for release improvements

[jviau]

Issue describing the changes in this PR

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR -- TODO
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)

Additional information

This PR refactors our build artifacts to support the upcoming release improvements. The changes are:

1. SiteExtension and Symbols are no longer zipped.
   • The release pipeline will be responsible for zipping after it has made any changes (such as inserting jittraces)
2. PrivateSiteExtension removed. A new script is now included which will transform site extension into the private site extension.
   • This reduces our artifact size significantly. Especially since private site extension is only occasionally needed.
3. Windows artifacts consolidated under a single drop_windows artifact.
   • this is so the release pipeline can download only a single artifact.
4. Release notes added to artifacts so the release pipeline can use them when creating a GitHub release
5. We produce a new file release.json as a build artifact in drop_windows. This is used by the release pipeline for creating the GitHub release.
   • This is created by the site extension project via a New-ReleaseJson.ps1 script
6. Linux artifacts renamed to drop_linux for consistency with windows drop.
7. Adds a custom GetFileHas_Custom msbuild task to work around an issue with file path length in the existing msbuild task.