chore: move cli/tests/ -> tests/ (#22369)

This looks like a massive PR, but it's only a move from cli/tests ->
tests, and updates of relative paths for files.

This is the first step towards aggregate all of the integration test
files under tests/, which will lead to a set of integration tests that
can run without the CLI binary being built.

While we could leave these tests under `cli`, it would require us to
keep a more complex directory structure for the various test runners. In
addition, we have a lot of complexity to ignore various test files in
the `cli` project itself (cargo publish exclusion rules, autotests =
false, etc).

And finally, the `tests/` folder will eventually house the `test_ffi`,
`test_napi` and other testing code, reducing the size of the root repo
directory.

For easier review, the extremely large and noisy "move" is in the first
commit (with no changes -- just a move), while the remainder of the
changes to actual files is in the second commit.

tests/unit_node/testdata/child_process_stdio.js

@@ -0,0 +1,16 @@
+import childProcess from "node:child_process";
+import process from "node:process";
+import * as path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const script = path.join(
+  path.dirname(fileURLToPath(import.meta.url)),
+  "node_modules",
+  "foo",
+  "index.js",
+);
+
+const child = childProcess.spawn(process.execPath, [script], {
+  stdio: [process.stdin, process.stdout, process.stderr],
+});
+child.on("close", () => console.log("close"));