Extended attributes

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Design API for reading, writing and enumerating extended attributes.
Potential API choices:

1. Handle EA operations via the original file/directory handle.
   • Pros:
     1. API simplicity.
     2. Parallel with POSIX fgetxattr.
   • Cons:
     1. Requires to re-open EA handle on windows for every call.
2. Open a separate EA handle (and cache EA metadata) that can operate as a view.
   • Pros:
     1. API flexibility (such as ranges support).
     2. Separation of concerns.
   • Cons:
     1. API complexity.