special handling for the JsonDescriptor to work around changes in PHP's JSON pretty printer
don't disable constructor calls to mockups of classes that extend internal PHP classes
minor #11191 [Tests] fix tests due to recent changes in PHP's behavior (xabbuh)

This PR was merged into the 2.4 branch.

Discussion
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[Tests] fix tests due to recent changes in PHP's behavior

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11176
| License       | MIT
| Doc PR        |

The drawback of this solution is that the pretty printed string produced by ``json_encode()`` isn't validated anymore. Instead, the tests only ensures that the represented object structure is as expected. I guess that's fair enough since the goal of the test is not to test PHP's pretty printing feature.

Commits
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bc8042d don't disable constructor calls to mockups of classes that extend internal PHP classes
f4a3c7a special handling for the JsonDescriptor to work around changes in PHP's JSON pretty printer