Add macro to check for required json keys

[DevwratJoshi]

1. LoadJsonValueByKey now returns a bool. If the key does not exist in the document the function will return false, else will return true.
2. A macro (MUJINCLIENTJSON_LOAD_REQUIRED_JSON_VALUE_BY_KEY) is added, wrapping LoadJsonValueByKey. If the keys are not in the document, an exception is thrown.

[cielavenir]

oh @DevwratJoshi actually you might need to port controllercommon!488 as well.

[cielavenir]

ask Yoshiki if required

[felixvd]

Is there a reason this is a macro instead of a function LoadRequiredJsonValueByKey?

[cielavenir]

ya, actually I also think function is better, then we can put it in a namespace...

[cielavenir]

should we talk in controllercommon!489 ?

[felixvd]

I see, Ziyan brought up the same concern here. Let's keep discussion here for now.

[felixvd]

That makes you, me and @ziyan arguing for a function over a macro then

[DevwratJoshi]

@cielavenir Yoshiki said that the changes from controllercommon!488 could be better, so they might be changed in the future.
We decided that it is best to be consistent across the 3 repos as far as possible though, so I have added the changes from that MR to this one as well. If we change that code block in one of the repos in the future, we will have to be sure to change all of them.

By the way, the behaviour in master for LoadJsonValueByKey is to return false if the key is present but the value is null (which will also throw an exception if the function is called via MUJINCLIENTJSON_LOAD_REQUIRED_JSON_VALUE_BY_KEY.
Do you think this is ok? We are basically assuming that required keys cannot have Null value.

[felixvd]

By the way, the behaviour in master for LoadJsonValueByKey is to return false if the key is present but the value is null (which will also throw an exception if the function is called via MUJINCLIENTJSON_LOAD_REQUIRED_JSON_VALUE_BY_KEY.
Do you think this is ok? We are basically assuming that required keys cannot have Null value.

My understanding is that Webstack will not distinguish between fields that are unset and fields that are set to null, and this behavior is in line with that.

cc @ziyan

[rdiankov]

Does anyone have any issues with this change? I don't.
Also, can we get the same change in the internal mujinjson.h file?
Thanks,