Warning on Open with VS2019 Plugin

[DylanCottell]

When opening Visual Studio 2019 with the new version of AxoCover, I get a warning saying "Visual Studio did not load one or more extensions that were using deprecated API's". It doesn't seem to affect anything however, and just seems to be a weird quirk.

[chrish619]

There is a PR to "solve" the issue with 2019 targets, #191

But seems like there is more work required to get this on the market place & Visual Studio 2019 16.1+

From @madskristensen:

https://devblogs.microsoft.com/visualstudio/updates-to-synchronous-autoload-of-extensions-in-visual-studio-2019/

By default, Visual Studio 2019 v16.1 blocks any synchronously autoloaded package from any extension and shows a notification to alert the user about it.

and:

Here’s a bullet list to sum it up:

• Marketplace requires autoload to be async and in the background
• Users and IT admins can opt out of the blocking behavior (not recommended)
• Autoloading extension should always happen asynchronously in the background

AsyncPackages are usable in VisualStudio 2015 (and above)
https://github.com/Microsoft/VSSDK-Extensibility-Samples/tree/master/AsyncPackageMigration

I can contribute to this issue, as I would also love to use AxoCover in VisualStudio 2019.