[HttpKernel] use static late binding when dumping out container
minor #9678 [HttpKernel] use static late binding when dumping out container (tgabi333)

This PR was submitted for the 2.2 branch but it was merged into the 2.3 branch instead (closes #9678).

Discussion
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[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)

Commits
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2e241cc [HttpKernel] use static late binding when dumping out container
Merge branch '2.3' into 2.4

* 2.3:
  Fixed typo
  [validator] throw an exception if isn't an instance of ConstraintValidatorInterface.
  Reset the box model to content-box in the web debug toolbar
  [FrameworkBundle] Allowed "0" as a checkbox value in the php template.
  raising delta on stopwatch as travis really breaks with less than 35
  Switched to correct gender of "Token"
  fixed typos in several translations
  [HttpKernel] use static late binding when dumping out container