This PR updates the `extension.toml` to allow specifying multiple
languages for a language server to work with.
The `languages` field takes precedence over `language`. In the future
the `language` field will be removed.
As part of this, the Emmet extension has been extended with support for
PHP and ERB.
Release Notes:
- N/A
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Co-authored-by: Max <max@zed.dev>