minor #36665 SCA: file_exists -> is_dir|is_file in foundation and kernel (kalessil)
minor #36665 SCA: file_exists -> is_dir|is_file in foundation and kernel (kalessil)

This PR was squashed before being merged into the 5.2-dev branch.

Discussion
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SCA: file_exists -> is_dir|is_file in foundation and kernel

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | n/a
| License       | MIT
| Doc PR        | n/a

Inspired by #36556 and replaces file_exists with is_dir|is_file alternative in order to leverage built-in cache advantages.

Commits
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0c467691b2 SCA: file_exists -> is_dir|is_file in foundation and kernel

symfony/http-foundation