quick-lint-js build sizes

Generate data.json by following these instructions:

1. Install LLVM, ensuring you have the llvm-size command.
2. Mount c.quick-lint-js.com using sshfs:

   $ mkdir -p ~/c.quick-lint-js.com/
   $ sshfs github-ci@c.quick-lint-js.com:/var/www/c.quick-lint-js.com/ ~/c.quick-lint-js.com/

3. Generate missing build-sizes.json files:

   $ go run tools/build-sizes/collect-many-binary-sizes.go ~/c.quick-lint-js.com/builds/

4. Create data.json:

   $ ./tools/build-sizes/aggregate-binary-sizes ~/c.quick-lint-js.com/builds/ >tools/build-sizes/data.json