internal/task: swap stack chain when switching goroutines

This change swaps the stack chain when switching goroutines, ensuring that the chain is maintained consistently.
This is only really currently necessary with asyncify on wasm.

src/internal/task/gc_stack_chain.go

@@ -0,0 +1,19 @@
+//go:build (gc.conservative || gc.extalloc) && tinygo.wasm && !scheduler.coroutines
+// +build gc.conservative gc.extalloc
+// +build tinygo.wasm
+// +build !scheduler.coroutines
+
+package task
+
+import "unsafe"
+
+//go:linkname swapStackChain runtime.swapStackChain
+func swapStackChain(dst *unsafe.Pointer)
+
+type gcData struct {
+	stackChain unsafe.Pointer
+}
+
+func (gcd *gcData) swap() {
+	swapStackChain(&gcd.stackChain)
+}