feat(rules): new rule `void-content`

...ules/__tests__/__snapshots__/void-content.md.spec.ts.snap

...ules/__tests__/__snapshots__/void-element.md.spec.ts.snap

docs/rules/__tests__/void-content.md.spec.ts

docs/rules/__tests__/void-element.md.spec.ts

docs/rules/void-content.md

elements/__snapshots__/html5.spec.ts.snap

src/config/__snapshots__/config-loader.spec.ts.snap

src/config/recommended.ts

src/engine/engine.spec.ts

src/rules/__snapshots__/void-content.spec.ts.snap

src/rules/void-content.spec.ts

src/rules/void-content.ts

test-files/config/.htmlvalidate.json