Object.assign documentation and tests

[jmagaram]

This took me a while because I wrote some tests to experiment and got the source and target mixed up - the mutable target goes first. Should we have labels on these?

I attempted to write code for assignMany but it doesn't work because you can't create an array of objects with different types. Well you can I guess if they start off as Object.empty() or are imported - jumping through hoops. Will this really get used? Do we need a toGenericObject function?

I couldnt' figure out the other flavor of assign with the json thing and what it does.

[zth]

Looking great!

Good point about assignMany. I think we can leave it undocumented for now. The Object module is for more specialized usage anyway.

[glennsl]

Adding assign2, assign3 etc. could be a good idea.

[glennsl]

But you can also just chain calls to assign, so... 🤷

[jmagaram]

Interesting idea on the assign2 assign3 - hadn't thought about that. I don't know when any of these functions will get used from ReScript, if ever. I wouldn't mind removing the assignMany and rely on chaining calls. A toUntypedObject could normalize objects in a list so assignMany will work. You all have much more real-world experience and know better what is needed here.

[jmagaram]

Consolidated into #117