Productize the ConPTY nuget package (for 3p use)

###### [original thread: #3577][initial PR: #12980]

ala #11865

Actually ship this thing as a supported nuget package.

When this and #6999 are done, go ingest the sample from #15053, because it's awesome.

```[tasklist]
### Pre-reqs
- [ ] #14000
```

```[tasklist]
### Tasks
- [ ] https://github.com/microsoft/terminal/issues/9462
- [ ] https://github.com/microsoft/terminal/issues/14477
- [ ] https://github.com/microsoft/terminal/issues/16911
- [ ] https://github.com/microsoft/terminal/issues/17822
```

Start by reviewing prerequisite issue #14000 and the task issues #9462, #14477, #16911, and #17822 to understand the required work for shipping ConPTY as a supported NuGet package. The issue is done when those prerequisites and tasks are complete and the package is ready for third-party use; then ingest the sample from #15053.

Written by the indexing model from the issue text.