[Validator] Made sure that context changes don't leak out of (Contextual)ValidatorInterface
[Validator] Fixed doc block
[Validator] Added markObjectAsInitialized() and isObjectInitialized() to ExecutionContextInterface
bug #11412 [Validator] Made sure that context changes don't leak out of (Contextual)ValidatorInterface (webmozart)

This PR was merged into the 2.5 branch.

Discussion
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[Validator] Made sure that context changes don't leak out of (Contextual)ValidatorInterface

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11046
| License       | MIT
| Doc PR        | -

Commits
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ff48939 [Validator] Added markObjectAsInitialized() and isObjectInitialized() to ExecutionContextInterface
14b60c8 [Validator] Fixed doc block
91bf277 [Validator] Made sure that context changes don't leak out of (Contextual)ValidatorInterface