Synthetic 'field' variable is no more created in extension property accessors #KT-9303 Fixed

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

@@ -0,0 +1,17 @@
+// See KT-9303: synthetic field variable does not exist for extension properties
+val String.foo: Int
+    get() {
+        // No shadowing here
+        val field = 42
+        return field
+    }
+
+val String.bar: Int = <!PROPERTY_INITIALIZER_NO_BACKING_FIELD!>13<!>
+    // Error
+    get() = <!UNRESOLVED_REFERENCE!>field<!>
+
+class My {
+    val String.x: Int = <!PROPERTY_INITIALIZER_NO_BACKING_FIELD!>7<!>
+        // Error
+        get() = <!UNRESOLVED_REFERENCE!>field<!>
+}