Add leak test project.

[danielcweber]

Inspired by https://github.com/reactiveui/website/blob/3da0fa9eabb6fd0052fd8f273fb3aab5dac16120/input/blog/2018-05-15-memory-leak-detection.md.

@onovotny @ghuntley Can you check CI integration please? Do we have access to dotMemory?

[ghuntley]

Dan - I'm happy to vouch for you and the work you are doing in opensource. Mash your deets into this https://www.jetbrains.com/buy/opensource/?product=resharper form and link back to this thread in the details. If you run into any issues lemme know and I'll speak with their dev advocates to make it happen.

[danielcweber]

Just to get this right - will it qualify me for a local subscription of ReSharper or will this enable us to use it in CI (VSTS)?

[danielcweber]

@onovotny Could you please review this line, it's rather clumsy and I don't know whether we would want the leak tests to be run with coverage analysis, or whether we would want to run "dotnet test" to cover all platforms, so I need some guidance. Thx!