Added general de/activation mechanism for plugins

[RunDevelopment]

The whole thing is implemented as a small isActive function prism-core.

This adds about 150bytes to Core and about 50bytes to Keep Markup but saves about 130bytes in LN and 40bytes in NW. So we gain a few bytes overall but we also gain functionality.

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This resolves #2433.

[LeaVerou]

LGTM. I may have done the implementation of isActive differently, e.g. in one of the following ways:

1. Use element.closest(`.${className}, .no-${className}`) and then examine what class the result has
2. Use element.closest(`.${className}`) and element.closest(`.no-${className}`) and then if both exist use element1.contains(element2)

But that's just optimization :)

[RunDevelopment]

I never heard of closest but with it (and some newer JS syntax) you can do the whole function in a one-liner:

function isActive(element, className, defaultActivation) {
    return element?.closest(`${className}, no-${className}`)?.classList?.contains(className) ?? defaultActivation;
}

Unfortunately, my favorite browser doesn't support it.

[LeaVerou]

I would avoid unsupported syntax, though I'm more lenient with unsupported functions, since they can always be polyfilled. And we're discussing dropping IE11 anyway, right?

Also if I'm reading the one liner above correctly, it looks like it would fail (would return true instead of false) if an element had no-classname and defaultActivation was true.

[RunDevelopment]

And we're discussing dropping IE11 anyway, right?

Yes, but we haven't yet.

Hmmm. Maybe it's a good idea to have a tracking issue of all things that should be done after we drop IE11?

Also if I'm reading the one liner above correctly, it looks like it would fail (would return true instead of false) if an element had no-classname and defaultActivation was true.

Nope, (false ?? true) === false. defaultActivation will only come into play if and any of the chained values is nullish.

[LeaVerou]

Hmmm. Maybe it's a good idea to have a tracking issue of all things that should be done after we drop IE11?

Absolutely.

Nope,

Oh right.