[Serializer] Added a test for decoding xml with whitespaces
minor #11233 [Serializer] Added a test for decoding xml with whitespaces (florianv)

This PR was merged into the 2.6-dev branch.

Discussion
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[Serializer] Added a test for decoding xml with whitespaces

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

The PR https://github.com/symfony/symfony/commit/466a3d70b7972dbac20264c254351ca31ee5c476 introduced a BC break because white spaces were previously decoded as text nodes.

So this PR reverts it and adds a context option to configure it.

Commits
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f5bf45e [Serializer] Added a test for decoding xml with whitespaces