Differentiate accessors by FieldAccessorKind

Otherwise accessors for backing fields (as in '{ field }') clash with
accessors for properties (as in '{ prop }').

 #KT-21258 Fixed Target versions 1.2.30

compiler/testData/codegen/box/syntheticAccessors/kt21258_indirect.kt

@@ -0,0 +1,8 @@
+class Foo {
+    private val fld: String = "O"
+        get() = { field }() + "K"
+
+    val indirectFldGetter: () -> String = { fld }
+}
+
+fun box() = Foo().indirectFldGetter()

compiler/testData/codegen/box/syntheticAccessors/kt21258_simple.kt

@@ -0,0 +1,12 @@
+class Foo {
+    private val fld: String = "O"
+        get() = { field }() + "K"
+
+    val indirectFldGetter: () -> String = { fld }
+
+    fun simpleFldGetter(): String {
+        return fld
+    }
+}
+
+fun box() = Foo().simpleFldGetter()