Improve serializer

[flobernd]

This PR updates the Elastic.Transport library and adjusts the DefaultRequestResponseSerializer and DefaultSourceSerializer implementations accordingly.

There are now multiple additional extension methods available in the Elastic.Transport.Extensions namespace which can be used for easiy (de-)serialization without having to know details about the underlaying serializer implementation:

• Deserialize(Serializer, JsonElement, Type, MemoryStreamFactory)
• Deserialize(Serializer, JsonNode, Type, MemoryStreamFactory)
• Deserialize(Serializer, ReadOnlySpan<Byte>, Type, MemoryStreamFactory)
• Deserialize(Serializer, ReadOnlySpan<Char>, Type, MemoryStreamFactory)
• Deserialize(Serializer, Utf8JsonReader&, Type, MemoryStreamFactory)
• Deserialize<T>(Serializer, JsonElement, MemoryStreamFactory)
• Deserialize<T>(Serializer, JsonNode, MemoryStreamFactory)
• Deserialize<T>(Serializer, ReadOnlySpan<Byte>, MemoryStreamFactory)
• Deserialize<T>(Serializer, ReadOnlySpan<Char>, MemoryStreamFactory)
• Deserialize<T>(Serializer, Utf8JsonReader&, MemoryStreamFactory)
• Serialize(Serializer, Object, Type, Utf8JsonWriter, MemoryStreamFactory, SerializationFormatting)
• Serialize(Serializer, Object, Type, Utf8JsonWriter, SerializationFormatting)
• Serialize<T>(Serializer, T, Utf8JsonWriter, MemoryStreamFactory, SerializationFormatting)
• Serialize<T>(Serializer, T, Utf8JsonWriter, SerializationFormatting)
• SerializeToBytes(Serializer, Object, Type, MemoryStreamFactory, SerializationFormatting)
• SerializeToBytes(Serializer, Object, Type, SerializationFormatting)
• SerializeToString(Serializer, Object, Type, MemoryStreamFactory, SerializationFormatting)
• SerializeToString(Serializer, Object, Type, SerializationFormatting)
• SerializeToBytes<T>(Serializer, T, MemoryStreamFactory, SerializationFormatting)
• SerializeToString<T>(Serializer, T, MemoryStreamFactory, SerializationFormatting)

Related to #8359