Release 4.0.0

[sylus]

See the full release documentation for more detail.

• [x] All related projects (wxt_library and wxt_bootstrap) tagged and released on GitHub.com and Drupal.org
• [x] Version number selected
• [x] CHANGELOG.md updated
• [x] composer.json updated
• [x] CI build passes
• [x] Releases tagged and pushed to GitHub.com and Drupal.org
• [x] WxT released on Drupal.org (https://github.com/drupalwxt/wxt/wiki/Release-process#release)
• [x] Add changelog information to published tag once CI is done