- writer test apitest suites are now called like the UNO implementation they
  are testing
- also mark them final for good measure
- move tests to module test and try to match its conventions
  * BaseIndex
  * TextDocumentIndex
  * TextDocumentSettings
  * TextPrinterSettings
  * TextSettings
  * XDocumentIndex
- also remove anonymous namespace in header, as that is a bad idea
- also remove now obsolete ApiBaseTest
- also remove dead code in TextPrinterSettings
- remove writer xtextcontent test as it duplicates the impl in module test

Change-Id: I71aa5f3755d5c90726f4ff4394117fa2391495d7
Reviewed-on: https://gerrit.libreoffice.org/69374
Tested-by: Jenkins
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@libreoffice.org>