Force svelte not to interpret some classes

[tobiasBora]

When using rehype-katex, it generates text like:

<div class="math math-inline">
 … some stuff involving {x} that is interpreted by svelte
</div>

and it produces error as {x} usually comes from a math expression like \sqrt{x} and is not meant to be replaced as a svelte variable. People created a rehype-katex-svelte (as recommended in #302) to solve this issue and this seems to work reasonably well, but I don't know how well maintained this is (e.g. it requires a quite old remark-math, but so do rehype-katex so it might be unrelated) and the author mention some potential security flows. As such, it seems not at battle-tested as rehype-katex.

As such, I was wondering if would instead directly allow users to add in MDsveX (via the options) a list of classes that should be wrapped around {@html } appropriately (with escaping etc) in order not to be interpreted by svelte later in the process. As rehype-katex does not want to do it on their side (see remarkjs/remark-math#104), I see not much other solution, and this might anyway be useful in other scenarios.