Add support for Sveltia CMS

**What problem does this solve?**
The [Sveltia CMS](https://sveltiacms.app/) currently does not have support in the Harper Chrome extension. It is [rapidly growing in popularity](https://sveltiacms.app/en/showcase) and would benefit immensely from Harper's capabilities.

**Proposed Solution**
I have a patch that enables support for it, but it has a couple of bugs that I'm still ironing out. My hacky version targeted the root element of its [Lexical](https://github.com/facebook/lexical)-based code editor so most of the text being processed is seen by Harper as a continuously running block of text making it do things like this:

**Examples**
Not sure what to put in here /shrug

**Component**
- [ ] Core engine
- [x] Plugin/Extension
- [ ] Other: _____

**Additional Context**
Any other relevant info.

No files or tests are named. Start by reviewing the Harper Chrome extension integration and the author's existing patch, then reproduce the behavior in Sveltia CMS's Lexical-based editor. Done means Sveltia text is processed correctly without being treated as one continuously running block.

Written by the indexing model from the issue text.