SpringBoot Add ThreadPoolTaskSchedulerBuilder as a replacement for TaskSchedulerBuilder

ThreadPoolTaskSchedulerBuilder will be a replacement for the to-deprecate TaskSchedulerBuilder. This is quite the same as #36637, but for TaskSchedulerBuilder. With #36609 we want to introduce a SimpleAsyncTaskScheduler.

Comment From: mhalbritter

The bean arrangement works this way:

If users don't have a custom TaskSchedulerBuilder: Both a TaskSchedulerBuilder and a ThreadPoolTaskSchedulerBuilder is available. The ThreadPoolTaskSchedulerBuilder applies the deprecated TaskSchedulerCustomizers, too. The ThreadPoolTaskSchedulerBuilder is used to build the ThreadPoolTaskScheduler.

If users have a custom TaskSchedulerBuilder: There's no ThreadPoolTaskSchedulerBuilder in the context, and the TaskSchedulerBuilder is used to build the ThreadPoolTaskScheduler.