Mitigate dependency upon ConfigCache
merged branch webfactory/issue-7230/picks/cache-file-utils (PR #7753)

This PR was squashed before being merged into the master branch (closes #7753).

Discussion
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Mitigate dependency upon ConfigCache

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes (refactoring)
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        | todo, issue is symfony/symfony-docs#2531

Some clients use ConfigCache only for its ability to atomically write into a file.

The PR moves that code into the Filesystem component.

It's a pick off #7230.

__To-Do:__
- [ ] Update docs for the Filesystem component

Commits
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3158c41 Mitigate dependency upon ConfigCache
[Config] added missing dep in composer.json