Issue #3409407 by quietone, smustgrave, xjm, longwave: Remove Book module from comments not in tests

Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2684319 by TravisCarden, jhodgdon: ConfigFormBaseTrait::config() @return doxygen is inaccurate

Issue #2392319 by alexpott, effulgentsia: Config objects (but not config entities) should by default be immutable