Formatting: Ignore chat separators with markdown

Some chat separators (or dinkuses) cause markdown to be rendered
on the chat window.

Examples include "###" -> h3 and "---" -> metadata.

This can look jarring to the end user as it can interrupt a pleasant
chat experience. Therefore, it makes sense to ignore these lines with
div tags that indicate to Showdown that this string doesn't need markdown.

Signed-off-by: kingbri <bdashore3@proton.me>

public/scripts/showdown-dinkus.js

@@ -0,0 +1,19 @@
+import { power_user } from './power-user.js';
+
+// Showdown extension to make chat separators (dinkuses) ignore markdown formatting
+export const dinkusExtension = () => {
+    if (!power_user) {
+        console.log("Showdown-dinkus extension: power_user wasn't found! Returning.");
+        return []
+    }
+
+    // Create an escaped sequence so the regex can work with any character
+    const savedDinkus = power_user.custom_chat_separator
+    const escapedDinkus = savedDinkus.split('').map((e) => `\\${e}`).join('');
+    const replaceRegex = new RegExp(`^(${escapedDinkus})\n`, "gm")
+    return [{
+        type: "lang",
+        regex: replaceRegex,
+        replace: (match) => match.replace(replaceRegex, `<div>${savedDinkus}</div>`).trim()
+    }];
+}