Support highlight syntax

[henrymcl]

Is your feature request related to a problem? Please describe.
Describe the solution you'd like
Support the extended syntax for highlights

Describe alternatives you've considered
Allowing HTML is too dangerous

Additional context
None

[calumk]

This works, you have to add it manually, as i havent submitted as a pull request yet.

import { Mark } from "@tiptap/core";


const Highlight = Mark.create({
    name: 'highlight',
});

export default Highlight.extend({
    /**
     * @return {{markdown: MarkdownMarkSpec}}
     */
    addStorage() {
        return {
            markdown: {
                serialize: {open: '==', close: '==', expelEnclosingWhitespace: true},
                parse: {
                    updateDOM(element) {
                        element.innerHTML = element.innerHTML.replace(/\=\=(.*?)\=\=/g, '<mark>$1</mark>')
                    },
                },
            },
        }
    }
});