Create internal .NET Project System SDK

## Summary

We have a lot of build logic duplicated (or almost duplicated) across our different repositories. This leads to several issues:

- It is difficult to tell what logic is core to a particular piece of build infrastructure (signing, localization, VSIX/NuGet/NPM packaging, testing, etc.) and what is a repo-specific modification to meet a particular need.
- Standing up a new repo is difficult as you need to figure out what to copy from a different repo.
- As best practices and/or the core tooling change it is difficult to update all the repos.
- While we have similar patterns across all (well, most) of our repos we don't have a single location where our infrastructure patterns are documented.

To address these issues we should pull out the core .props, .targets, and PowerShell scripts used by our build into a NuGet-based SDK, and then update all of our repos to consume that SDK.

Start by inventorying the duplicated .props, .targets, and PowerShell build scripts described in the issue, along with the repositories that consume them. Done means the shared build logic is packaged as a NuGet-based SDK and the repositories are updated to consume it.

Written by the indexing model from the issue text.