feat: switch to remark from markdown-it (big)

* replaces old mentions with avatar and display name
* renders things directly through React
* replaces most of the markdown hacks with custom AST components
* adds a tooltip to codeblock "copy to clipboard"

src/components/common/Emoji.tsx

@@ -1,3 +1,5 @@
+import { emojiDictionary } from "../../assets/emojis";
+
 export type EmojiPack = "mutant" | "twemoji" | "noto" | "openmoji";
 
 let EMOJI_PACK: EmojiPack = "mutant";
@@ -40,7 +42,7 @@ function toCodePoint(rune: string) {
         .join("-");
 }
 
-function parseEmoji(emoji: string) {
+export function parseEmoji(emoji: string) {
     if (emoji.startsWith("custom:")) {
         return `https://dl.insrt.uk/projects/revolt/emotes/${emoji.substring(
             7,