PocoDoc: search support

[vrabac6]

The PocoDoc did not support integration with FTS5 SQLite database for the purpose of inputting clean content into the database. To enhance its functionality, the following improvements have been implemented:

1. Expanded the writeDescription method by adding an output stream containing clean content.
2. Introduced a new method named writeSearchIndex , responsible for retrieving textual documentation along with links. This method is called within existing methods writeClass , writePackage , and writeNameSpace