Extract Clojure support into an extension (#10088)

This PR extracts Clojure support into an extension and removes the
built-in Clojure support from Zed.

Release Notes:

- Removed built-in support for Clojure, in favor of making it available
as an extension. The Clojure extension will be suggested for download
when you open a `.clj` or other Clojure-related files.

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Co-authored-by: Max <max@zed.dev>