fix(unstable): Honor granular unstable flags in js runtime (#21466)

This fixes #21434 for `BroadcastChannel` and `WebSocketStream`.
`--unstable` still enable both, but granular unstable flags now also
work:

* `--unstable-net` now enables `WebSocketStream`.
* `--unstable-broadcast-channel` now enables `BroadcastChannel`.
* Additionally, there are now tests for all granular unstable flags.
Since `unsafe-proto` already had tests, so I didn't add any for this
one.

It also introduces a map to keep track of granular unstable ids without
having to sync multiple places.

1 files changed, 10 insertions, 0 deletions

diff --git a/cli/tests/testdata/run/unstable_broadcast_channel.js b/cli/tests/testdata/run/unstable_broadcast_channel.js
new file mode 100644
index 000000000..b8576aa22
--- /dev/null
+++ b/cli/tests/testdata/run/unstable_broadcast_channel.js
@@ -0,0 +1,10 @@
+const scope = import.meta.url.slice(-7) === "#worker" ? "worker" : "main";
+
+console.log(scope, globalThis.BroadcastChannel);
+
+if (scope === "worker") {
+  postMessage("done");
+} else {
+  const worker = new Worker(`${import.meta.url}#worker`, { type: "module" });
+  worker.onmessage = () => Deno.exit(0);
+}