Rename tests: singular + generic (#3880)

* Fix #3347

* Rename data->singular, schema->generic

* Rm schema, data flag + tag behavior

* Update test FQNs, compiled paths

* Add changelog entry

automatic commit by git-black, original commits:
  a5ce658
  ca7c1fc

core/dbt/task/test.py

@@ -126,9 +126,7 @@ def before_execute(self):
         self.print_start_line()
 
     def execute_test(
-        self,
-        test: Union[CompiledSingularTestNode, CompiledGenericTestNode],
-        manifest: Manifest
+        self, test: Union[CompiledSingularTestNode, CompiledGenericTestNode], manifest: Manifest
     ) -> TestResultData:
         context = generate_runtime_model_context(
             test, self.config, manifest