Description:
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SQLite3 provides Online Backup API (https://www.sqlite.org/backup.html) for copying databases in safe way. Please expose the API through the SQLite3 extension.

Test script:
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$source = SQLite3('original.sqlite');
$dest = SQLite3('backup.sqlite');

  # equivalent of C sqlite3_backup_init()
$backup = new SQLite3Backup($dest, $source);

  # equivalent of C sqlite3_backup_step()
$backup->step($npages = -1);

  # equivalent of C sqlite3_backup_finish
$backup->finish();

echo 'backup complete.';

Expected result:
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backup complete.

Actual result:
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class SQLite3Backup does not exist