feat: make text expander aware of custom emojis

The old MDE editor is aware of custom emojis and shows them as
suggestions, but the new text expander is not aware of them and seems to
re-implement some logic.

Simplify it by using what `emoji.js` already provides.

Custom emojis require a bit more work to get shown correctly (HTML and
adding a `gap` to fake a space).

web_src/js/features/emoji.js

@@ -10,6 +10,7 @@ for (const {emoji, aliases} of emojis) {
 }
 
 export const emojiKeys = Object.keys(tempMap).sort((a, b) => {
+  if (b === '+1' && a === '-1') return 1;
   if (a === '+1' || a === '-1') return -1;
   if (b === '+1' || b === '-1') return 1;
   return a.localeCompare(b);