runtime: run syscall/js finalizers on wasm without a manual GC (#5545)

* runtime: run syscall/js finalizers on wasm without a manual GC

* runtime: address review feedback on finalizer idle GC

* runtime: clear a finished task's args pointer so its arguments are collectable

* runtime: skip the finalizer scan with a per-block registration bit

* runtime: guard the finalizer registration bitmap with gcLock

* testdata: cover finalizer invariants on every scheduler

* main_test: limit the finalizer scheduler variants to linux and darwin

* testdata: wait for the finalizer queue to drain before asserting

* testdata: make the finalizer counters atomic and wait for a known drain count

* runtime: add finalizer bookkeeping asserts under runtime_asserts

* runtime: address finalizer GC review feedback

* testdata: strengthen blocked stack finalizer test

* runtime: fix finalizer cleanup edge cases

* runtime: decouple wasm export scheduling from finalizers

* runtime: avoid redundant wakeups for re-entrant wasm exports

* runtime: simplify finalizer comments

testdata/wasmexport-finalizer.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"runtime"
+	"syscall/js"
+)
+
+//go:wasmimport tester finalizerRan
+func finalizerRan()
+
+//go:wasmimport tester backgroundRan
+func backgroundRan()
+
+//go:wasmimport tester callNestedExport
+func callNestedExport()
+
+var nestedCallback js.Func
+
+//go:wasmexport launchBackground
+func launchBackground() {
+	go func() {
+		backgroundRan()
+	}()
+}
+
+//go:wasmexport installNestedCallback
+func installNestedCallback() {
+	nestedCallback = js.FuncOf(func(js.Value, []js.Value) any {
+		callNestedExport()
+		return nil
+	})
+	js.Global().Set("nestedExportCallback", nestedCallback)
+}
+
+//go:noinline
+func registerFinalizersImpl() {
+	for i := 0; i < 32; i++ {
+		p := new([2]int)
+		runtime.SetFinalizer(p, func(*[2]int) { finalizerRan() })
+	}
+}
+
+//go:wasmexport registerFinalizers
+func registerFinalizers() {
+	registerFinalizersImpl()
+	go func() {
+		backgroundRan()
+	}()
+}
+
+func main() {}