NI: Support forking inference with heuristics

Mostly, it only affects FIR

It partially allows to consider several variance of constraints like
A<Int> & A<T> <: A<X_var> that are mostly brought by smart casts

^KT-49542 Fixed
^KT-50489 Relates

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -13809,6 +13809,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/inference/selectOfLambdaWithExtensionEnabled.kt");
             }
 
+            @Test
+            @TestMetadata("smartCastFork.kt")
+            public void testSmartCastFork() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inference/smartCastFork.kt");
+            }
+
             @Test
             @TestMetadata("specialCallsWithCallableReferences.kt")
             public void testSpecialCallsWithCallableReferences() throws Exception {
@@ -36673,6 +36679,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/testsWithStdLib/inference/kt4975.kt");
             }
 
+            @Test
+            @TestMetadata("plusAssignOnArrayList.kt")
+            public void testPlusAssignOnArrayList() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/inference/plusAssignOnArrayList.kt");
+            }
+
             @Test
             @TestMetadata("recursiveFlexibleAssertions.kt")
             public void testRecursiveFlexibleAssertions() throws Exception {