Wintersmith is no longer maintained given that the most recent version
is from six years ago, and all vulnerabilities that NPM reports
originate from Wintersmith's dependencies. Metalsmith, and its plugins,
on the other hand have recently had releases and don't have known
vulnerabilities. In fact, the number of reported vulnerabilities by NPM
even goes down to zero with this patch applied.
This commit therefore replaces Wintersmith with Metalsmith by providing
a transparent drop-in replacement, in a way that requires the least
amount of changes to the code and the generated output.
Note that this patch does update our versions of jQuery, Bootstrap and
the Highlight.js theme because the previous versions were very outdated
and didn't work correctly with Metalsmith. Moreover, those old versions
contained vulnerabilities that are hereby fixed.
Fixes#18198.
The examples themselves were updated to account for JavaScript modules, which didn't require changing the actual URLs.
However, since it seems that JSFiddle doesn't support JavaScript modules in its separate "JavaScript" editing-area we need to change how we embed the examples to avoid showing a blank "JavaScript"-tab.
This is essentially a simplified version of the code that's used in `PDFPageView`, which will hopefully reduce the number of issues opened specifically about blurry rendering.
However, note that *ideally* users should base their implementations on the `components/` examples rather than using the API directly (the "viewer components" already support HiDPI-screens).
