Update emoji data for Unicode 16 (#36596)

Use emoji data from https://github.com/github/gemoji/pull/303 because
`github/gemoji` is unmaintained.

`assets/emoji.json` is now pretty-printed so that future diffs will
actually be readable. This causes no isses as the only place where it is
used is in frontend which imports it via `with {type: 'json'}` where
whitespace is irrelevant.

<img width="205" height="75" alt="image"
src="https://github.com/user-attachments/assets/96e335b8-acf6-4996-ace4-824c0870a7d3"
/>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

build/generate-emoji.go

@@ -24,8 +24,8 @@ import (
 )
 
 const (
-	gemojiURL         = "https://raw.githubusercontent.com/github/gemoji/master/db/emoji.json"
-	maxUnicodeVersion = 15
+	gemojiURL         = "https://raw.githubusercontent.com/rhysd/gemoji/537ff2d7e0496e9964824f7f73ec7ece88c9765a/db/emoji.json"
+	maxUnicodeVersion = 16
 )
 
 var flagOut = flag.String("o", "modules/emoji/emoji_data.go", "out")
@@ -149,8 +149,8 @@ func generate() ([]byte, error) {
 	}
 
 	// write a JSON file to use with tribute (write before adding skin tones since we can't support them there yet)
-	file, _ := json.Marshal(data)
-	_ = os.WriteFile("assets/emoji.json", file, 0o644)
+	file, _ := json.MarshalIndent(data, "", "  ")
+	_ = os.WriteFile("assets/emoji.json", append(file, '\n'), 0o644)
 
 	// Add skin tones to emoji that support it
 	var (