[formrecognizer] Refactor DAC tests into separate files (Azure#21968)

* refactor async prebuilt analyze tests

* clean up refactored tests and recordings

* refactor async url analyze prebuilt tests

* add recordings for async url tests

* refactor sync prebuilt analyze tests

* add new recordings, delete old ones

* refactor sync analyze prebuilt from url tests

* add new url test recordings and delete old ones

* remove unused imports

* rename general document and layout tests

* update general document and layout recordings

* refactor custom documents tests, update recordings

Author: catalinaperalta