Remove Vue ESLint plugin for Vite compatibility

The Vue ESLint plugin is not compatible with Vite and isn't provided in
Vite's default template. By removing it, the codebase progresses toward
the migration to Vue 3.0 and Vite (#230).

Changes:

- Directly execute `eslint` in the `npm run lint:eslint` command.
- Fix previously undetected linting issues that weren't covered by Vue
  CLI's default configuration.
- Updated various configuration files, reflecting the removal and lint
  fixes.
- Remove unused `eslint-plugin-import` dependency that is already
  imported by `@vue/eslint-config-airbnb-with-typescript`.

In `.eslintrc.cjs`:

- Add `es2022` as environment in to simplify setting parser options and
  align with Vite starter configuration.
- Remove useless tests override.
- Move tests override in root `.eslintrc.cjs` to `tests/` for clarity,
  better organization, scalability and separation of concerns.

tests/.eslintrc.cjs

@@ -0,0 +1,5 @@
+module.exports = {
+  rules: {
+    'no-console': 'off',
+  },
+};