JVM IR: Mark lateinit fields as NotNull

This is needed for compatibility with the JVM backend.

compiler/testData/codegen/bytecodeListing/lateInitNotNull.kt

@@ -0,0 +1,5 @@
+// Test to ensure that we mark the backing field of a lateinit property
+// as NotNull, even though the field is nullable in the JVM IR backend.
+class A {
+    lateinit var x: A
+}