[EuiMarkdownFormat] Lacks support for modern `:emoji:`

**Reported by**

@aarju

**Describe the bug**

`EuiMarkdownFormat` does not handle all supported `:emoji:`, which are used often in responses from Agents

**Environment and versions**

- EUI version: 112.1.0

**To Reproduce**

1. go to [Markdown / Format](https://eui.elastic.co/docs/components/editors-and-syntax/markdown/format/) in the docs
2. open the Source of the example and type `:robot:`

**Expected behavior**

All supported text `:emoji:` are converted to emoji e.g. `:smile:` → :smile:

**Screenshots (Optional)**

**Additional context**

Upgrading the `remark-emoji` package to v4 or higher should fix it — but it's ESM-only and requires Node >= 18, so upgrading the package requires extra changes