[Finder] added Finder::ignoreUnreadableDirs() method
merged branch jfsimon/issue-6981 (PR #7518)

This PR was merged into the master branch.

Discussion
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[Finder] adds a way to ignore AccessDeniedException

This PR adds a `Finder::ignoreUnreadableDirs()` method which tells `Finder` to ignore unreadable directories instead of throwing an `AccessDeniedException`.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #6981

Commits
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a63b30b [Finder] added Finder::ignoreUnreadableDirs() method
[Finder] updated CHANGELOG