feat: add locale composable

[nekosaur]

Description

creates locale and rtl composables.

adapter helpers for vue-i18n and vue-intl are not included here since it would mean we'd need to depend on those packages. they should probably be separate npm packages that can be imported and used.

resolves #13539

Motivation and Context

v3

How Has This Been Tested?

playground. still needs tests

Markup:

<template>
  <v-app class="fill-height">
    <v-locale-provider :locale="scoped" :rtl="true">
      <Foo />
    </v-locale-provider>

    <Foo />

    <span>global: {{ t('$vuetify.close') }}</span>

    <button @click="current = current === 'ja' ? 'sv' : 'ja'">toggle</button>
    <button @click="scoped = scoped === 'ja' ? 'sv' : 'ja'">toggle</button>
    <pre>{{ current }}</pre>
    <pre>isRtl: {{ isRtl }}</pre>
    <input v-model="scoped">
  </v-app>
</template>

<script>
  import { h, ref } from 'vue'
  import { useLocale } from '../src/composables/locale'
  import { useRtl } from '../src/composables/rtl'

  const Foo = {
    props: {
      bar: {
        type: null,
      },
    },
    setup (props, ctx) {
      const locale = useLocale()
      const { isRtl } = useRtl()

      return () => h('div', [
        h('div', ['translated: ' + locale.t('$vuetify.close')]),
        h('div', [`isRtl: ${isRtl.value}`]),
        ctx.slots.default?.(),
      ])
    },
  }

  export default {
    name: 'Playground',
    components: { Foo },
    setup () {
      const locale = useLocale()
      const scoped = ref('sv')
      const { isRtl } = useRtl()

      return { ...locale, scoped, isRtl }
    },
  }
</script>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)

[glen-84]

I prefer vue-intl (Format.JS). vue-i18n is still optional, right?

[nekosaur]

Yes, it's optional. And the API here is still very much up in the air. I'll have a look at vue-intl.

[nekosaur]

@glen-84 I've reworked the adapter interface to kind of work with vue-intl as well. still very prototypey.

[nekosaur]

This or some version of locale/rtl needs to be merged pretty soon