Improve test coverage of quantity methods with unit system parameter

[angularsen]

Improve test coverage with +2.65% up to 83.11% by testing generated code that take the UnitSystem as parameter.

https://codecov.io/gh/angularsen/UnitsNet/pull/844/changes

• Add new test base class UnitsNet.Tests.TestsBase.QuantityTestsBase with abstract bool SupportsSIUnitSystem { get; }
• Declare SI unit system compatibility for each quantity's base test class
• Generate test cases for ctor, As() and ToBaseUnit()
• Remove duplicate, hard coded test cases in QuantityTests.Ctor.cs
• Define base units for Volume.CubicMeter in order to pass test, seemed missing

[angularsen]

Not sure why codecov bot does'nt create the report, maybe because I only touched test-code.
Coverage is up 2.65% to 83.11%

https://codecov.io/gh/angularsen/UnitsNet/pull/844/changes