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

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

@@ -0,0 +1,9 @@
+class My(val field: Int) {
+    // Backing field, initializer
+    val second: Int = 0
+        get() = field
+
+    // No backing field, no initializer
+    val third: Int
+        get() = this.field
+}