Introduce Variable: Use expression unifier to find duplicates

idea/testData/refactoring/introduceVariable/OccurrencesInStringTemplate.kt

@@ -0,0 +1,4 @@
+fun a(x: Int) {
+    val a = <selection>x + 1</selection>
+    "it's a number ${x + 1}"
+}

idea/testData/refactoring/introduceVariable/OccurrencesInStringTemplate.kt.after

@@ -0,0 +1,5 @@
+fun a(x: Int) {
+    val i = x + 1
+    val a = i
+    "it's a number ${i}"
+}

idea/testData/refactoring/introduceVariable/UnresolvedOccurrences.kt

@@ -0,0 +1,7 @@
+fun a() {
+    val x = <selection>Foo()</selection>
+    println(Foo())
+    println(Foo)
+    println(Foo(1))
+    println(1.Foo())
+}

idea/testData/refactoring/introduceVariable/UnresolvedOccurrences.kt.after

@@ -0,0 +1,8 @@
+fun a() {
+    val foo = Foo()
+    val x = foo
+    println(foo)
+    println(Foo)
+    println(Foo(1))
+    println(1.Foo())
+}