Fix issues with `FileSupport.GetCanonicalPath()` extension method

[NightOwl888]

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• I have searched the existing issues

Task description

There are currently several issues with the implementation of FileSupport.GetCanonicalPath(), which is mostly a port from Apache Harmony. This method is on a required path for nearly all users, so it would be good to ensure that it is optimized and fully functional.

• No guard clause for null check, which should throw ArgumentNullException
• Logic is allocating 1 extra byte to the temporary array, appending a 0 byte at the end, converting to string, then removing the trailing \0 character that the 0 byte creates. It would be better just to omit the null character from the buffer.
• The part that resolves symbolic links was not ported (there is a LUCENENET TODO for it in the code).
• The behavior of the GetOrAdd() method already allows racing threads to both run the business logic without blocking. If we move the logic that builds the string into the factory parameter of this method, we can eliminate the extra TryGetValue() check (and the unnecessary check for a null string in the collection).
• J2N.Text now contains an extension method for Encoding that accepts a Span<byte> so we can allocate the temporary buffer on the stack on all supported target frameworks.