Remove default values from initializers

[namolnad]

Improves clarity and prevents mistakes showcased in #1460 by removing default values for initializers

[apollo-cla]

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[designatednerd]

I think this is generally a good start - I want to do some more rethinking before an official release is cut, since I think there's still some pretty significant opportunities for developers to accidentally have different stores.

May wait a day or two to merge this until I have that bit ready to go, but overall, this is a great start 👍

[designatednerd]

I poked at what my idea was and it was WAY over-complex. This is much more straightfoward, so let's go with this approach. I'll update some docs post-merge.

[namolnad]

Sounds great — glad it was helpful. Thanks for looking at it!