Improve emoji and mention matching (#24255)

Prioritize matches that start with the given text, then matches that
contain the given text.

I wanted to add a heart emoji on a pull request comment so I started
writing `:`, `h`, `e`, `a`, `r` (at this point I still couldn't find the
heart), `t`... The heart was not on the list, that's weird - it feels
like I made a typo or a mistake. This fixes that.

This also feels more like GitHub's emoji auto-complete.

# Before

![image](https://user-images.githubusercontent.com/20454870/233630750-bd0a1b76-33d0-41d4-9218-a37b670c42b0.png)

# After

![image](https://user-images.githubusercontent.com/20454870/233775128-05e67fc1-e092-4025-b6f7-1fd8e5f71e87.png)

---------

Signed-off-by: Yarden Shoham <git@yardenshoham.com>
Co-authored-by: silverwind <me@silverwind.io>

web_src/js/utils/match.test.js

@@ -0,0 +1,47 @@
+import {test, expect} from 'vitest';
+import {matchEmoji, matchMention} from './match.js';
+
+test('matchEmoji', () => {
+  expect(matchEmoji('')).toEqual([
+    '+1',
+    '-1',
+    '100',
+    '1234',
+    '1st_place_medal',
+    '2nd_place_medal',
+  ]);
+
+  expect(matchEmoji('hea')).toEqual([
+    'headphones',
+    'headstone',
+    'health_worker',
+    'hear_no_evil',
+    'heard_mcdonald_islands',
+    'heart',
+  ]);
+
+  expect(matchEmoji('hear')).toEqual([
+    'hear_no_evil',
+    'heard_mcdonald_islands',
+    'heart',
+    'heart_decoration',
+    'heart_eyes',
+    'heart_eyes_cat',
+  ]);
+
+  expect(matchEmoji('poo')).toEqual([
+    'poodle',
+    'hankey',
+    'spoon',
+    'bowl_with_spoon',
+  ]);
+
+  expect(matchEmoji('1st_')).toEqual([
+    '1st_place_medal',
+  ]);
+});
+
+test('matchMention', () => {
+  expect(matchMention('')).toEqual(window.config.tributeValues.slice(0, 6));
+  expect(matchMention('user4')).toEqual([window.config.tributeValues[3]]);
+});