Add UnprocessableEntityHttpException to HttpKernel Exceptions
minor #10527 [HttpKernel] [Exception] Add UnprocessableEntityHttpException to HttpKernel Exceptions (steveYeah)

This PR was merged into the 2.5-dev branch.

Discussion
----------

[HttpKernel] [Exception] Add UnprocessableEntityHttpException to HttpKernel Exceptions

Add UnprocessableEntityHttpException, as this would have been useful as few times now.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
-------

304cbe9 Add UnprocessableEntityHttpException to HttpKernel Exceptions