Fix for KT-12127: Undeclared type variable on delegated property backing field

#KT-12127 Fixed

compiler/testData/writeSignature/backingFieldForGenericDelegated.kt

@@ -0,0 +1,18 @@
+import kotlin.reflect.KProperty
+import kotlin.reflect.KProperty1
+
+class DVal<T, R, P: KProperty1<T, R>>(val kmember: P) {
+    operator fun getValue(t: T, p: KProperty<*>): R {
+        return kmember.get(t)
+    }
+}
+
+class Value<T>(var text: String? = null)
+
+class Test {
+    val <T> Value<T>.additionalText by DVal(Value<T>::text)
+}
+
+// field: Test::additionalText$delegate
+// jvm signature: LDVal;
+// generic signature: null