[Translation] made XliffFileDumper support CDATA sections.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | maybe
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11256
| License       | MIT

why do you use CDATA over escaping the chars using `htmlspecialchars`?