feat(storage-plugin): use state classes as keys

[arturovt]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngxs/store/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

Foreword ❗

The key option was very unclear for most of our users. Most people got confused of what the heck is this option and how to use. That's why we had some issues and I made PRs to improve documentation.

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This PR scatters cloud and gives our users the ability to provide state classes except of strings. For sure it's still possible to provide strings as this might be a breaking change.

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This feature is a good alternative as it's preferred to have state keys only in one place.

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It could seem like there is a lot of code added, but no. I moved token factories to the separate internals.ts file, because storage.module.ts file became bigger and bigger. I've only added the transformKeyOption function that retrieves state metadatas from state classes.

So the compiled code is still very small.

[splincode]

The best!!!

[arturovt]

@splincode

Thanks man ❤️

The only thing I don't like is (stateClass as any)[OPTIONS_KEY].name :(

[splincode]

@markwhitfeld please review it)

[markwhitfeld]

Approved. Just a few small cosmetic tweaks.