[DependencyInjection] Use DOM instead of SimpleXML for namespace support
[DependencyInjection] Deprecate SimpleXMLElement
feature #10619 [DependencyInjection] Use DOM instead of SimpleXML for namespace support (sandermarechal, romainneutron)

This PR was merged into the 2.5-dev branch.

Discussion
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[DependencyInjection] Use DOM instead of SimpleXML for namespace support

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #9345
| License       | MIT

This PR replaces #9350

Commits
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a3c60c8 [DependencyInjection] Deprecate SimpleXMLElement
33c91f9 [DependencyInjection] Use DOM instead of SimpleXML for namespace support