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

compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -7919,6 +7919,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/coroutines/kt50277.kt");
         }
 
+        @TestMetadata("kt51718.kt")
+        public void testKt51718() throws Exception {
+            runTest("compiler/testData/codegen/box/coroutines/kt51718.kt");
+        }
+
         @TestMetadata("lastExpressionIsLoop.kt")
         public void testLastExpressionIsLoop() throws Exception {
             runTest("compiler/testData/codegen/box/coroutines/lastExpressionIsLoop.kt");