[Nightly] EUI i18n tokens in nightly Kibana PR

[weronikaolejniczak]

Summary

Closes https://github.com/elastic/eui-private/issues/750

Fixes the recurring nightly build failure caused by EUI i18n token changes not being propagated to Kibana's i18n_eui_mapping.tsx: elastic/kibana#279387

• Adds scripts/sync_kibana_i18n.mjs - a Node.js script that diffs two i18ntokens.json files and patches Kibana's mapping file:
  • adds missing entries (plain or arrow-function depending on interpolation),
  • removes deleted entries,
  • and updates changed defaultMessage values,
• adds two steps to the update_kibana_dependencies__prepare_changes.yml workflow:
  • "save current EUI i18n tokens" (before dep update): fetches i18ntokens.json from EUI GitHub at the version currently installed in Kibana; falls back to eui_last_release for snapshot versions;
  • "sync EUI i18n tokens" (after bootstrap): fetches the script from EUI at eui_ref, runs it and if the mapping changed - runs jest --updateSnapshot and commits the result as a separate chore: sync EUI i18n tokens commit.

Test plan

• Trigger nightly workflow manually with workflow_dispatch against a ref where tokens changed
• Verify chore: sync EUI i18n tokens commit appears in the Kibana PR when tokens differ
• (optional) Verify no extra commit when tokens are unchanged
• Verify the Kibana i18n lint check passes in CI after the sync commit

🤖 Generated with Claude Code

[infra-vault-gh-plugin-prod]

💚 Build Succeeded

• Buildkite Build
• Commit: 0d6b7f6

cc @weronikaolejniczak

[infra-vault-gh-plugin-prod]

💚 Build Succeeded

• Buildkite Build
• Commit: 0d6b7f6
• Documentation website
• Storybook
• 🚫 Visual regression tests skipped (remove the skip-vrt label to re-enable)

cc @weronikaolejniczak