Unifier: Fix matching of callable references with expression receivers

#KT-21334 Fixed

idea/testData/unifier/equivalence/expressions/callableReferences/expressionReceivers.kt

@@ -0,0 +1,14 @@
+public fun String.bar() = ""
+
+fun foo() {
+    val f = if (1 < 2) {
+        <selection>"abc"::bar</selection>
+    } else {
+        "def"::bar
+    }
+    val ff = if (1 < 2) {
+        ("abc")::bar
+    } else {
+        ("def")::bar
+    }
+}

idea/testData/unifier/equivalence/expressions/callableReferences/expressionReceivers.kt.match

@@ -0,0 +1,3 @@
+"abc"::bar
+
+("abc")::bar