Generate CHECKCAST after ACONST_NULL in coroutines

If we do not do this, the state-machine builder will not know the type
of the ACONST_NULL, defaulting to Object, leading to VerifyError.
Alternatively, we could use LVT to deduce the type, but getting types
from LVT is something I got rid of long time ago, and I have no desire
to return it back.

Generating CHECKCAST hints the state-machine builder the type of the
variable avoiding the issue of VerifyError. However, this CHECKCAST
replaces StrictBasicValue.NULL_VALUE with BasicValue in
OptimizationBasicInterpreter. To preserve optimization on not-spilling
known nulls, introduce BasicValues, which represent typed nulls and
create BasicInterpreter, which is aware of them. This way we have the
best of two worlds - we do not spill known nulls, and we know the type
of ACONST_NULL.

 #KT-51718 Fixed

native/native.tests/tests-gen/org/jetbrains/kotlin/konan/blackboxtest/NativeCodegenBoxTestGenerated.java

@@ -8041,6 +8041,12 @@ public class NativeCodegenBoxTestGenerated extends AbstractNativeCodegenBoxTest
                 runTest("compiler/testData/codegen/box/coroutines/kt49168.kt");
             }
 
+            @Test
+            @TestMetadata("kt51718.kt")
+            public void testKt51718() throws Exception {
+                runTest("compiler/testData/codegen/box/coroutines/kt51718.kt");
+            }
+
             @Test
             @TestMetadata("lastExpressionIsLoop.kt")
             public void testLastExpressionIsLoop() throws Exception {