PR: #2050

Support fmt.Stringer in getFunctionName

Description

Currently, getFunctionName only supports raw strings or function pointers.
If a caller passes a custom type that implements fmt.Stringer (e.g. a named type alias), it is treated as a function and causes error and hard to get the idea why:

INF log/with_logger.go:45 Task processing failed with error Namespace=default TaskQueue=chat-agent WorkerID=28030@Lukas-MacBook-Pro-M4.local@ WorkerType=WorkflowWorker Error="BadScheduleActivityAttributes: ActivityType is not set on ScheduleActivityTaskCommand. ActivityID=15"

Example

type ActivityName string

func (a ActivityName) String() string {
	return string(a)
}

var agentPlannerActivity ActivityName = "AgentPlannerActivity"

fut := workflow.ExecuteActivity(ctx, agentPlannerActivity, inputs{})