Restore previous behavior in GxFile.Open method

[claudiamurialdo]

Change previous fix on #1103 that involved retries, as it altered the expected behavior of the API (issue 204015).
Allow simultaneous read and write access to the file:

• Updated _fileStreamWriter to use FileShare.Read to allow read access while writing.
• Updated _fileStreamReader to use FileShare.ReadWrite to allow both read and write access.
• Ensured that the file can be accessed for reading and writing simultaneously without conflicts.

Issue:204015
Issue:203334

[genexusbot]

Cherry pick to beta success

• 5438c20