Support ESLint 9

[diskdance]

ESLint 9 release link: https://eslint.org/blog/2024/04/eslint-v9.0.0-released/

It contains breaking changes, like making flat config the new default (related issue: #94).

ESLint migration documentation:

• https://eslint.org/docs/latest/use/migrate-to-9.0.0
• https://eslint.org/docs/latest/use/configure/migration-guide

Issues of dependencies:

• Support ESLint 9 eslint-config-wikimedia#563