Infer reflection configuration for TestContextBootstrapper implementations

[snicoll]

The boot-features sample fail atm with the following:

 Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.boot.test.autoconfigure.web.client.RestClientTestContextBootstrapper]: No default constructor found; nested exception is java.lang.NoSuchMethodException: org.springframework.boot.test.autoconfigure.web.client.RestClientTestContextBootstrapper.<init>()
       org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:29)
       org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:176)
       org.springframework.test.context.BootstrapUtils.resolveTestContextBootstrapper(BootstrapUtils.java:147)
       [...]
     Caused by: java.lang.NoSuchMethodException: org.springframework.boot.test.autoconfigure.web.client.RestClientTestContextBootstrapper.<init>()
       java.lang.Class.getConstructor0(DynamicHub.java:3349)
       java.lang.Class.getDeclaredConstructor(DynamicHub.java:2553)
       org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:25)
       [...]

We should be able to infer the implementations that require to be instantiated via reflection.