text: Title: Change the parsing model object produced by `Test Tags` (and `Force Tags`) to `TestTags`
  Body: We are gong to rename `Force Tags` to `Test Tags` (#4365) and as the first step adding `Test Tags` as an alias for `Force Tags` in RF 5.1 (#4368). There were no other code changes and currently `Test Tags` (and `Force Tags`) is parsed into a `ForceTags` object. This should be changed to `TestTags` in RF 5.2.
  
  The change doesn't affect test execution at all, but tools working with the parsing model are affected. Luckily it's pretty easy to handle both objects by having both `visit_ForceTags` and `visit_TestTags` in a model visitor.
  