Kx-serialization: support SerialInfo for JVM IR

No tests added because this is going to be checked by the upcoming build
of kotlinx-serialization runtime with JVM IR.

 #KT-42976 In Progress

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/codegen/ExpressionCodegen.kt

@@ -218,7 +218,9 @@ class ExpressionCodegen(
             mv.visitLineNumber(1, startLabel)
         }
         val info = BlockInfo()
-        val body = irFunction.body!!
+        val body = irFunction.body
+            ?: error("Function has no body: ${irFunction.render()}")
+
         generateNonNullAssertions()
         generateFakeContinuationConstructorIfNeeded()
         val result = body.accept(this, info)