FIR IDE: fix shortenings for enums

idea/testData/shortenRefsFir/quailfiers/Enum.kt

@@ -0,0 +1,10 @@
+// FIR_COMPARISON
+package test
+
+enum class A {
+    B
+}
+
+fun usage() {
+    <selection>test.A.B</selection>
+}

idea/testData/shortenRefsFir/quailfiers/Enum.kt.after

@@ -0,0 +1,10 @@
+// FIR_COMPARISON
+package test
+
+enum class A {
+    B
+}
+
+fun usage() {
+    A.B
+}