[reflect] Fix flaky tests that depend on Reflection.clearCaches()

* Use ReflectionFactoryImpl as single point of synchronization
* Synchronize all cache-sensitive tests on it in order to be robust in parallel test runners
* Remove redundant cache clear after each test

Merge-request: KT-MR-6842
Merged-by: Vsevolod Tolstopyatov <qwwdfsad@gmail.com>

compiler/tests-common/tests/org/jetbrains/kotlin/codegen/AbstractBlackBoxCodegenTest.java

@@ -21,7 +21,6 @@ import java.io.File;
 import java.lang.reflect.Method;
 import java.util.List;
 
-import static org.jetbrains.kotlin.codegen.TestUtilsKt.clearReflectionCache;
 import static org.jetbrains.kotlin.test.KotlinTestUtils.assertEqualsToFile;
 import static org.jetbrains.kotlin.test.clientserver.TestProcessServerKt.getBoxMethodOrNull;
 import static org.jetbrains.kotlin.test.clientserver.TestProcessServerKt.getGeneratedClass;
@@ -100,9 +99,6 @@ public abstract class AbstractBlackBoxCodegenTest extends CodegenTestCase {
                 }
                 throw ExceptionUtilsKt.rethrow(e);
             }
-            finally {
-                clearReflectionCache(generatedClassLoader);
-            }
         }
         fail("Can't find box method!");
     }