Add SiteExtension.proj to replace build-extension.ps1

[jviau]

Issue describing the changes in this PR

resolves #issue_for_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 introduces a new project WebHost.Script.SiteExtension, which is a replacement for build-extension.ps1. This project can be used via dotnet CLI to restore, build, and publish all the artifacts needed for the Antares site extension. Note that this project has support for multi-targeting, but only targets a single TFM. This is in preparation for porting to in-proc branch to keep the diff minimal between the two.

Other Changes

• Removes update-hostreferences.ps1, this is no longer used anywhere
• Groups all worker versions into workers.props file. Left python out due to code owners, but ideally python will be moved there as well.
• zip-after-publish is extracted into a set of re-usable targets ZipPublish.targets.
• RuntimeIdentifiers added to WebHost.csproj. Having this set of identifiers listed improves the restore task (otherwise each time you want to use a different runtime, you have to re-restore).

[kshyju]

Approving to unblock.

[fabiocav]

Left a few comments. Reviewed best I could based on the nature of the changes. Can we please make sure this is rebased on latest and compare the artifact output to ensure we're good (assuming this was already done, but worth calling out).

[kamperiadis]

@jviau Just as a heads up, we have recently updated the java worker version so that appears to be causing conflicts for your PR.