Drop support for vue-i18n v8

[ota-meshi]

Tell us about your environment

• ESLint version: v9.4.0
• eslint-plugin-vue version: v9.24.1
• eslint-plugin-vue-i18n version: v3.2.0
• Node version: v22.4.1

The problem you want to solve.

Your take on the correct solution to problem.

Drop support for vue-i18n v8.

Additional context

We can remove https://github.com/intlify/eslint-plugin-vue-i18n/blob/master/lib/utils/message-compiler/parser-v8.ts.
There may be other rule options we can remove that I haven't listed yet.