fix class attr warning for SnackPlayer and on multiple pages

[Simek]

Why

Address class attr warning spotted in the dev console caused by SnackPlayer and platform tags on multiple pages.

How

Replace class attr with className in SnackPlayer component and for all platform tags used in docs content files.

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[cortinico]

That's a really long PR. I've skimmed through it and it looks good at first. I suppose this was automatically done and no other modifications are included

[Simek]

I can confirm that there are no other changes than class => className replace. I have to use regex replace on all MD files in /docs and /website/versioned_docs to address that issue, due to how many instance there were to correct. And after applying the fixes I have run format:markdown script.