Types on i18n global instance are too strict

[mehcode]

Reporting a bug?

if (!i18n.global.availableLocales.includes(locale)) {

TS2345: Argument of type 'string' is not assignable to parameter of type '"en"'.

---

Best I can tell, the availableLocales type is being resolved to an array of exactly the locals that exist when constructed. That's not ideal for

Expected behavior

No type errors.

Reproduction

Follow the lazy loading guide - https://vue-i18n.intlify.dev/guide/advanced/lazy.html#lazy-loading - in a TypeScript file.

System Info

System:
    OS: macOS 12.5.1
    CPU: (10) arm64 Apple M1 Max
    Memory: 3.20 GB / 64.00 GB
    Shell: 3.5.1 - /opt/homebrew/bin/fish
  Binaries:
    Node: 18.9.0 - /opt/homebrew/bin/node
    npm: 8.19.1 - /opt/homebrew/bin/npm
  Browsers:
    Chrome: 105.0.5195.102
    Firefox: 103.0.2
    Safari: 15.6.1
  npmPackages:
    @intlify/vite-plugin-vue-i18n: 7.0.0-beta.2 => 7.0.0-beta.2
    @vitejs/plugin-vue: ^3.1.0 => 3.1.0
    @vue/compiler-sfc: ^3.2.39 => 3.2.39
    @vue/server-renderer: ^3.2.39 => 3.2.39
    @vue/test-utils: ^2.0.2 => 2.0.2
    @vue/tsconfig: ^0.1.3 => 0.1.3
    vite: ^3.1.0 => 3.1.0
    vite-plugin-package-version: ^1.0.2 => 1.0.2
    vite-ssr: ^0.16.0 => 0.16.0
    vitest: ^0.23.2 => 0.23.2
    vue: ^3.2.39 => 3.2.39
    vue-eslint-parser: ^9.1.0 => 9.1.0
    vue-i18n: 9.3.0-beta.3 => 9.3.0-beta.3
    vue-router: ^4.1.5 => 4.1.5
    vue-tsc: ^0.40.13 => 0.40.13

### Screenshot

_No response_

### Additional context

_No response_

### Validations

- [X] Read the [Contributing Guidelines](https://github.com/intlify/vue-i18n-next/blob/master/.github/CONTRIBUTING.md)
- [X] Read the [Documentation](https://vue-i18n.intlify.dev/)
- [X] Check that there isn't [already an issue](https://github.com/intlify/vue-i18n-next/issues) that reports the same bug to avoid creating a duplicate.
- [X] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/intlify/vue-i18n-next/discussions)
- [X] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.