feat(rules): new rule `area-alt`

docs/rules/__tests__/__snapshots__/area-alt.md.spec.ts.snap

docs/rules/__tests__/area-alt.md.spec.ts

docs/rules/area-alt.md

docs/wcag.md

elements/__snapshots__/html5.spec.ts.snap

elements/html5.js

src/config/presets/a11y.ts

src/config/presets/recommended.ts

src/config/presets/standard.ts

src/rules/__snapshots__/area-alt.spec.ts.snap

src/rules/area-alt.spec.ts

src/rules/area-alt.ts

src/rules/index.ts

test-files/elements/area-invalid.html

test-files/elements/area-valid.html