"field": synthetic variable creation in accessors, codegen changed accordingly, a set of tests, relevant code fix (j2k)

compiler/testData/diagnostics/tests/backingField/FieldShadow.kt

@@ -0,0 +1,8 @@
+class My {
+    // No initialization needed because no backing field
+    val two: Int
+        get() {
+            val <!NAME_SHADOWING!>field<!> = 2
+            return field
+        }
+}