Add a component parameter builder or make param helpers more easily accessible

[egil]

Related to #5, where support for new test libs is planned, it will probably be a good idea to make it easier for users wanting to pass parameters to CUTs to do so without having to inherit from a base class in their tests, e.g. following the pattern of:

public void TestMethod()
{
    using var ctx = new TestContext();
    var params = new ComponentParameterBuilder(this) // 'this' might be needed to capture the execution context for callback parameters.
        .With("name", value)
        .WithCallback("name", () => {})
        .WithCascadingValue(obj)
        .WithChildContent("<p>hello world</p>")
        // ... etc
        .Build(); // Build could be done implicitly through a implicit conversion to ComponentParameter[]
    ctx.RenderComponent(params);
}