[finder] Introduced AccessDeniedException

This exception is thrown when trying to open a non-readable directory.

Squashed commits:
[Finder] Fixed small errors
[Finder] small changes about AccessDeniedException
[Finder] removed unnecessary comment
[Finder] added access denied exception test
[Finder] Updated AccessDeniedException base class
[Finder] fixed access denied exception test
[Finder] native adapters now throw AccessDeniedException on stderr
merged branch jfsimon/finder-access-denied-exception (PR #7256)

This PR was merged into the master branch.

Discussion
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[Finder] Adds AccessDeniedException

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

Commits
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714ace8 [finder] Introduced AccessDeniedException
[Finder] added a CHANGELOG entry for the previous merge