[Test] Add ability to mark group of tests with specific tags

Currently tags can be applied to all tests in specific testdata
  directory by placing `_tags.txt` file in it, where all tags should
  be listed on separate lines. Test generator adds those tags to
  corresponding generated test classes with `@Tag` annotation

Please note that is applicable only to JUnit 5 tests

compiler/tests-common/tests/org/jetbrains/kotlin/generators/impl/TestGeneratorImpl.kt

@@ -176,6 +176,9 @@ private class TestGeneratorImplInstance(
 
                 override val imports: Set<Class<*>>
                     get() = super.imports
+
+                override val tags: List<String>
+                    get() = emptyList()
             }
         }