core: introduce extensions (#9800)

Extensions allow declarative extensions to "JsRuntime" (ops, state, JS or middleware).

This allows for:
- `op_crates` to be plug-and-play & self-contained, reducing complexity leaked to consumers
- op middleware (like metrics_op) to be opt-in and for new middleware (unstable, tracing,...)
- `MainWorker` and `WebWorker` to be composable, allowing users to extend workers with their ops whilst benefiting from the other infrastructure (inspector, etc...)

In short extensions improve deno's modularity, reducing complexity and leaky abstractions for embedders and the internal codebase.

1 files changed, 9 insertions, 0 deletions

diff --git a/cli/tests/unit/metrics_test.ts b/cli/tests/unit/metrics_test.ts
index 9fa37e99b..25c63dbc1 100644
--- a/cli/tests/unit/metrics_test.ts
+++ b/cli/tests/unit/metrics_test.ts
@@ -69,3 +69,12 @@ unitTest(
     assert(metrics.opsDispatchedAsync === metrics.opsCompletedAsync);
   },
 );
+
+// Test that ops from op_crates have metrics (via OpMiddleware)
+unitTest(function metricsForOpCrates(): void {
+  const _ = new URL("https://deno.land");
+
+  const m1 = Deno.metrics().ops["op_url_parse"];
+  assert(m1.opsDispatched > 0);
+  assert(m1.opsCompleted > 0);
+});