Add Visual Studio 2019 enhanced themes

[JoeRobich]

I think themes based on the enhanced colors scheme introduced in VS2019 (dotnet/roslyn#31976) would be a nice addition.

Dark+

Light+

[nosami]

Looks great with F# code too

[JoeRobich]

Do I need to push this branch to origin so that CI can run? Or does it matter since this isn't a functional change?

[nosami]

Do I need to push this branch to origin so that CI can run? Or does it matter since this isn't a functional change?

We don't run CI from forks for security reasons. You could request access to the Mono org but I'll create a branch to save some time.

[sevoku]

It's not enough to add the json files, we also need to register the resources in the project file, so that the editor and preferences can pick them up. @sandyarmstrong could you help with that?

[JoeRobich]

Thanks @sevoku. I think I found the right spot to add them.

[JoeRobich]

@sevoku I installed the build produced by the CI. The themes were available from the preferences dialog and worked as expected.

[JoeRobich]

@sandyarmstrong Please let me know if there is anything else needed for this PR. =)

[sandyarmstrong]

@JoeRobich nothing needed from you, thanks. @jmatthiesen was a consensus reached with regard to naming so we can get this merged?

[jmatthiesen]

We're looking at having these replace the default Light and Dark themes, after merging in a few other fixes from the existing Visual Studio Light theme. To clean things up, I think it would be great to merge this work in from the external fork, and then I'll setup a new PR with the next set of changes. @sandyarmstrong, sound good?