Add script for setting up WASI dependencies (#9078)

This PR adds a script for setting up the WASI dependencies needed for
extensions.

These already get downloaded when needed when using Zed, but in the
tests the HTTP client is faked out, so if you don't already have them
installed the `test_extension_store_with_gleam_extension` test will
fail.

Release Notes:

- N/A

.github/workflows/ci.yml

@@ -89,6 +89,9 @@ jobs:
       - name: cargo clippy
         run: cargo xtask clippy
 
+      - name: Install WASI dependencies
+        run: script/setup-wasm
+
       - name: Run tests
         uses: ./.github/actions/run_tests