Add flag to force loading old inference diagnostics

compiler/tests-common/tests/org/jetbrains/kotlin/checkers/BaseDiagnosticsTest.kt

@@ -217,7 +217,7 @@ abstract class BaseDiagnosticsTest : KotlinMultiFileTestWithJava<TestModule, Tes
                 computeJvmSignatureDiagnostics(bindingContext)
 
             val ok = booleanArrayOf(true)
-            val withNewInference = newInferenceEnabled && withNewInferenceDirective
+            val withNewInference = newInferenceEnabled && withNewInferenceDirective && !USE_OLD_INFERENCE_DIAGNOSTICS_FOR_NI
             val diagnostics = ContainerUtil.filter(
                     CheckerTestUtil.getDiagnosticsIncludingSyntaxErrors(
                             bindingContext, implementingModulesBindings, ktFile, markDynamicCalls, dynamicCallDescriptors, withNewInference
@@ -324,6 +324,9 @@ abstract class BaseDiagnosticsTest : KotlinMultiFileTestWithJava<TestModule, Tes
 
         val WITH_NEW_INFERENCE_DIRECTIVE = "WITH_NEW_INFERENCE"
 
+        // Change it to "true" to load diagnostics for old inference to test new inference (ignore diagnostics with <NI; prefix)
+        private val USE_OLD_INFERENCE_DIAGNOSTICS_FOR_NI = false
+
         private fun parseDiagnosticFilterDirective(directiveMap: Map<String, String>, allowUnderscoreUsage: Boolean): Condition<Diagnostic> {
             val directives = directiveMap[DIAGNOSTICS_DIRECTIVE]
             val initialCondition =