feature #18036 [Serializer] XmlEncoder: Make load flags configurable (dunglas)
feature #18036 [Serializer] XmlEncoder: Make load flags configurable (dunglas)

This PR was squashed before being merged into the 3.1-dev branch (closes #18036).

Discussion
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[Serializer] XmlEncoder: Make load flags configurable

| Q             | A
| ------------- | ---
| Branch        | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #17987
| License       | MIT
| Doc PR        | todo

Commits
-------

0826068 [Serializer] XmlEncoder: Make load flags configurable

symfony/serializer,symfony/Serializer