Added new Not all plugin

[RunDevelopment]

This adds a new plugin Not all with allows to filter out certain elements the highlightAll and highlightAllUnder methods query.

This adds a new filter property to the env of before-highlightall which can be used to add filters. I named it filter because it very much behaves like Array#filter.

This also exposes getLanguage as Prism.util.getLanguage.

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@asbjornu
My attempt to fix #2068.

[asbjornu]

Thanks for this, @RunDevelopment! Much appreciated! 🙏

[asbjornu]

I just thought that it would be completely awesome if this was possible to configure in a data- attribute on the <script> element, so no custom JavaScript was necessary and the data-manual attribute could be removed.

[RunDevelopment]

Done. Now you can do the following:

<script src="prism.js" data-exclude-css=".no-highlight, .no-highlight *"></script>

This will exclude all element with a .no-highlighting class and all elements in a element with a .no-highlighting class.

As for the original issue: You can either use filterKnown:

<script src="prism.js" data-filter-known></script>

Or define a filter function:

<script src="prism.js"></script>
<script>
Prism.plugins.notAll.filter(({ language }) => language !== 'mermaid');
</script>

[asbjornu]

@RunDevelopment, Fantastic! 🎉 Thank you so much! 🙏

[mAAdhaTTah]

Sorry I took so long to get to this. Thanks for your patience!

[mAAdhaTTah]

Just need to bikeshed some naming here but the code itself is great! Thanks for your patience.

[RunDevelopment]

Should be good to go now.

[mAAdhaTTah]

That took some massaging, but this looks good to me! Thanks for the work on this. One more PR to go for this release...