Fix OG images containing <s (among others) displaying text with escaped characters (<).

This fix is taken directly (and adapted) from the code I wrote in Svelte Changelog (here then here), as we use the same core logic and I encountered the exact same issue. :D

Before (svelte.dev)	After (localhost)

Notes on the code

• I took advantage of the existing escape.js file to add in my (opposite) logic, which is exactly made for this purpose (lucky me!). In the existing code, I lifted the regex out of the function so it can be computed only once, and made it dynamic so that everything derives from the single existing record. I also added more characters to the record. Finally, I added a null check to the existing function to avoid any problem, even though it'll very likely never be used!
• I duplicated the vnode logic to both the OG image generators, as a bunch of the logic is already duplicated between both, and I don't really know where to put it anyway; it's very dependent on the very computing code in the core of the generators. Let me know if you have any suggestions!

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