chore(testrunner): Add abstractions to decouple from VSTest

[MarcZw]

Why?

Stryker should be able to support other testrunners apart from VSTest.
This is not possible in the current implementation of Stryker, because of the tight coupling with VSTest.
Therefore some abstractions needed to be created to facilitate the decoupling from VSTest.

Solution

The current solution to decouple is to introduce a new project, Stryker.Shared.
This project contains abstractions to facilitate other testrunners, without breaking the current implementation.

Note this is a temporary solution. There are plans for an architectural overhaul, to decouple Stryker even more.

[sonarcloud]

Quality Gate failed

Failed conditions
79.2% Coverage on New Code (required ≥ 80%)
36 New Code Smells (required ≤ 2)
1 New Critical Issues (required ≤ 0)
32 New Major Issues (required ≤ 0)
3 New Minor Issues (required ≤ 0)
1 New Security Hotspots (required ≤ 0)

See analysis details on SonarCloud

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