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
+}

compiler/testData/codegen/bytecodeListing/lateInitNotNull.txt

@@ -0,0 +1,7 @@
+@kotlin.Metadata
+public final class A {
+    public @org.jetbrains.annotations.NotNull field x: A
+    public method <init>(): void
+    public final @org.jetbrains.annotations.NotNull method getX(): A
+    public final method setX(@org.jetbrains.annotations.NotNull p0: A): void
+}