Currently, all the pages in the double write files are unencrypted. Even pages
belonging to encrypted tablespaces, remain unencrypted in the double write
files. The purpose of this worklog is to ensure that the pages in double write
files belonging to encrypted tablespaces are also encrypted. Likewise, the
pages in dblwr files that belong to unencrypted tablespace remain unencrypted.
There is no separate encryption key for the double write files. The pages are
encrypted making use of the respective tablespace encryption keys. The same
encrypted page that will be written to the data file of a tablespace is also
written to the double write file. The high level steps would be:

* If transparent compression is enabled for a tablespace, do compression.
* If encryption is enabled for a tablespace, do encryption using the tablespace key.
* Flush the compressed+encrypted page to the dblwr file.
* Flush the same compressed+encrypted page to the data file of tablespace.

The double write files now contain different types of pages depending on the
tablespaces. Some of them are unencrypted, some are encrypted with their
respective tablespaces keys, and the remaining are compressed+encrypted with
their respective tablespace keys.

rb#24072 approved by Mayank Prasad <mayank.prasad@oracle.com>
and Sunny Bains <sunny.bains@oracle.com>