[HttpKernel] use static late binding when dumping out container

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no?
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |  #9649
| License       | MIT
| Doc PR        | 

This PR gives the ability to override the stripComments method in descendants (and to disable the memory-eater container whitespace stripping)