Implement an abstract class for MSBuild Tasks to support dependency injection

[missymessa]

Based on this conversation here: #6526 (comment)

Providing an abstract class for MSBuild Task classes to implement will help support dependency injection in MSBuild Tasks. This should make it easier to bootstrap DI into existing MSBuild tasks so that we can mock out external dependencies when we write unit tests for the MSBuild Tasks.

Link to Chad's gist as a proof-of-concept for this: https://gist.github.com/ChadNedzlek/6b5ef4aa380e8d262539c5489348d3c1

[missymessa]

I did this already! :)

https://github.com/dotnet/arcade/blob/main/src/Common/Microsoft.Arcade.Common/MSBuildTaskBase.cs