Process and run a single ready timer macrotask. This function should be registered through Deno.core.setMacrotaskCallback. Returns true when all ready macrotasks have been processed, false if more ready ones are available. The Isolate future would rely on the return value to repeatedly invoke this function until depletion. Multiple invocations of this function one at a time ensures newly ready microtasks are processed before next macrotask timer callback is invoked.