Add a `JsonObject.TryAdd` method.

[eiriktsarpalis]

This workaround requires dual lookup if the key is missing, which suggests to me that a JsonObject.TryAddmethod similar to the one in #107947 might be necessary.

Originally posted by @eiriktsarpalis in dotnet/aspire#6312 (comment)

API Proposal

Exposing the APIs as approved for OrderedDictionary to JsonObject:

namespace System.Text.Json.Nodes;

public partial class JsonObject
{
    public bool TryAdd(string propertyName, JsonNode? value, out int index);
    public bool TryGetPropertyValue(string propertyName, out JsonNode? jsonNode, out int index);
}

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[terrajobst]

Video

• Looks good as proposed but we should add an overload of TryAdd without the index for consistency and ergonomics
• The behavior of what we return for the index should match OrderedDictionary<TKey, TValue>

namespace System.Text.Json.Nodes;

public partial class JsonObject
{
    public bool TryAdd(string propertyName, JsonNode? value);
    public bool TryAdd(string propertyName, JsonNode? value, out int index);
    public bool TryGetPropertyValue(string propertyName, out JsonNode? jsonNode, out int index);
}