Resolves#3286
1. `lean4.json` → `lean4.tmLanguage`
1. Download `vscode-lean4/syntaxes/lean4.json` from https://github.com/leanprover/vscode-lean4/pull/623 (now merged).
2. Install the VS Code extension [TextMate Languages (pedro-w)](https://marketplace.visualstudio.com/items?itemName=pedro-w.tmlanguage).
3. Open `lean4.json` in VS Code, <kbd>F1</kbd>, and “Convert to tmLanguage PLIST File”.
2. `lean4.tmLanguage` → `lean4.sublime-syntax`
Open `lean4.tmLanguage` in Sublime text, “Tools → Developer → New Syntax from lean4.tmLanguage…”.