Async configuration ignores `applicationTaskExecutor` when `EnableScheduling` is enabled

[snicoll]

If you enable both @EnableScheduling and @EnableAsync it looks like the async processing is detecting the taskScheduler as a candidate for async processing.

This leads to

2019-01-17 07:53:16.174  INFO 48078 --- [   scheduling-1] .s.a.AnnotationAsyncExecutionInterceptor : More than one TaskExecutor bean found within the context, and none is named 'taskExecutor'. Mark one of them as primary or name it 'taskExecutor' (possibly as an alias) in order to use it for async processing: [applicationTaskExecutor, taskScheduler]

and the auto-configured applicationTaskExecutor is ignored and replaced by the simple AsyncTaskExecutor.

[snicoll]

Closing in favour of PR #15748