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

src/runtime/runtime_wasmentry.go

@@ -7,7 +7,6 @@ package runtime
 // compiler for //go:wasmexport support.
 
 import (
-	"internal/task"
 	"unsafe"
 )
 
@@ -85,19 +84,3 @@ func wasmExportRun(done *bool) {
 		runtimePanic("//go:wasmexport function did not finish")
 	}
 }
-
-// Called from the goroutine wrapper for the //go:wasmexport function. It just
-// signals to the runtime that the //go:wasmexport call has finished, and can
-// switch back to the wasmExportRun function.
-//
-// This function is not called when the scheduler is disabled.
-func wasmExportExit() {
-	// Signal to the scheduler that it should return, since this call to a
-	// //go:wasmexport function has exited.
-	schedulerExit = true
-
-	task.Pause()
-
-	// TODO: we could cache the allocated stack so we don't have to keep
-	// allocating a new stack on every //go:wasmexport call.
-}