Add `displayName` option for Provider

[kyleshevlin]

Because the Provider is created inside the closure of generateContext, it's generically named Provider. So even though you give it a variable name when you destructure it, it still shows up as Provider in your React dev tools. Adding an option for displayName would make this a bit better.

I believe this can be achieved by:

• [ ] adding providerDisplayName as an option
• [ ] Default it to undefined or null, just a falsy value that makes sense
• [ ] if (providerDisplayName) Provider.displayName = providerDisplayName
• [ ] Updating docs

[kyleshevlin]

It should be noted, that one can add a display name very simply on their own if they need it, this would just be a convenience to the user. They are, of course, welcome to do:

const [MyProvider, useMyContext] = generateContext(useManageValue)
MyProvider.displayName = 'MyProvider'