extend array/dictionary functionally

[peno64]

• Add interator on LWJsonArray such that a foreach can be done over an array object
• Implement ContainsKey to check if a key exists

[progklb]

Sorry for such a late reply on this! Life has been quite busy and I haven't looked at my personal projects in a while.

Thank you for the PR. I just wanted to discuss the reasoning behind some changes :)

• Although adding a LWJson.ContainsKey is useful for overrides in key/value pair types, I don't see how it makes sense for pure arrays or value types. This is why I added it specifically to the LWJsonObject type, as it can represent key-value pairs. Are there cases where we would need ContainsKey for these other types?

• I like the idea of adding the enumerator to the base LWJson - this is useful for LWJsonArray, as well as LWJsonObject, as we could return the value for each entry in the dictionary. However, I feel this gets a bit messy LWJsonValue as these can be pure value types (float, int, bool) and are not suitable for enumeration. Maybe a string-specific enumerator would be okay, but then the LWJson return type of this enumerator isn't suitable. So ultimately I feel like this isn't suitable as a base-class method.

Keen to hear your thoughts!