Rust: add test setup script

rust/ql/test/setup.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+set -euo pipefail
+
+# This script is run by the CI to set up the test environment for the Rust QL tests
+# We run this as rustup is not meant to be run in parallel, and will this setup will be run by rust-analyzer in the
+# parallel QL tests unless we do the setup prior to launching the tests.
+# We do this for each `rust-toolchain.toml` we use in the tests (and the root one in `rust`)
+
+cd "$(dirname "$0")"
+
+rustup install
+rustup component add rust-src
+
+find . -name rust-toolchain.toml \
+  -execdir rustup install \; \
+  -execdir rustup component add rust-src \;