Add PR workflow build

[timheuer]

This adds a GitHub Actions workflow for pull requests only as a start (so no publish to VSIX gallery). Emulates current workflow and steps used by the VSIX powershell scripts but only uses one snippet of that and now embedded in the workflow (probably a generic pattern replace action that could even be replaced with but the pwsh script does the job and is fast)

[madskristensen]

Thanks Tim. It does look like a lot of boilerplate needed here in initial setup of .NET, NuGet and MSBuild. I wonder if there is a way to have a base file that this inherit from? I notice you do something like that here:

- name: Set version for Visual Studio Extension
  uses: cezarypiatek/VsixVersionAction@1.0

I don't know if it is possible, but if that could be cleaned up so you only need to take care of building, testing, and uploading from the individual .yaml file would be awesome.

[timheuer]

I wonder if there is a way to have a base file that this inherit from? I notice you do something like that here:

There isn't today an action that does that but there is ability to use composite actions so it looks like one step. This is new for Actions, but I'll set it up

[timheuer]

Okay, added some more composite actions to better templatize the bootstrapping and encapsulate the version logic you had previously.

[madskristensen]

It's starting to look pretty awesome. Is it read to be merged?

[madskristensen]

Yay, thanks @timheuer