Allow setting property names comparer in DeepEqual.System.Text.Json

[mariusz96]

I would like to have an option for these two to equal:

using DeepEqual;
using DeepEqual.Syntax;
using DeepEqual.SystemTextJson;
using System.Text.Json;

var object1 = JsonDocument.Parse("""{"Object":{"Property":1}}""");
var object2 = JsonDocument.Parse("""{"object":{"property":1}}""");

var comparison = new ComparisonBuilder()
    .UseSystemTextJson()
    .Create();

bool result = object1.IsDeepEqual(object2, comparison);

object1.ShouldDeepEqual(object2, comparison);

It would likely need to be implemented here:

DeepEqual/src/DeepEqual.System.Text.Json/JsonElementComparison.cs

Lines 64 to 65 in 78f91a4

	var properties1 = leftValue.EnumerateObject().ToDictionary(x => x.Name);
	var properties2 = rightValue.EnumerateObject().ToDictionary(x => x.Name);