Update TheoryData in v2 with new support from v3

[bradwilson]

The v3 TheoryData class includes new constructors and methods that are missing in v2, per #2836. Example:

xunit/src/xunit.core/TheoryData.cs

Lines 40 to 50 in 36fe729

	public class TheoryData<T> : TheoryData
	{
	/// <summary>
	/// Adds data to the theory data set.
	/// </summary>
	/// <param name="p">The data value.</param>
	public void Add(T p)
	{
	AddRow(p);
	}
	}

xunit/src/xunit.v3.core/TheoryData.cs

Lines 53 to 86 in 5b64d0e

	public class TheoryData<T> : TheoryData
	{
	/// <summary>
	/// Initializes a new isntance of the <see cref="TheoryData{T}"/> class.
	/// </summary>
	/// <param name="values">The initial set of values</param>
	public TheoryData(IEnumerable<T> values)
	{
	Guard.ArgumentNotNull(values);
	AddRange(values.ToArray());
	}
	/// <summary>
	/// Initializes a new isntance of the <see cref="TheoryData{T}"/> class.
	/// </summary>
	/// <param name="values">The initial set of values</param>
	public TheoryData(params T[] values) =>
	AddRange(values);
	/// <summary>
	/// Adds data to the theory data set.
	/// </summary>
	/// <param name="p">The data value.</param>
	public void Add(T p) =>
	AddRow(p);
	/// <summary>
	/// Adds multiple data items to the theory data set.
	/// </summary>
	/// <param name="values">The data values.</param>
	public void AddRange(params T[] values) =>
	AddRows(values.Select(x => new object?[] { x }));
	}

[bradwilson]

Available in v2 2.6.5-pre.2 https://xunit.net/docs/using-ci-builds