Kotlin examples in Spring Core docs should use extension functions with reified types

**Affects:**  5.2.0-SNAPSHOT

In https://github.com/spring-projects/spring-framework/tree/master/src/docs/asciidoc/core line 374 is:
```
val service = context.getBean("petStore", PetStoreService::class.java)
```

"Kotlin style" would be:
```
val service = context.getBean<PetStoreService>("petStore")
```
