IR:

- Redo smart casts handling (yet again).
Front-end typing information can't be used for expressions in IR,
since it provides inferred type for PSI expressions for the last corresponding resoled call.

- Assignments handling, initial implementation.

compiler/testData/ir/irText/smartCastsWithDestructuring.kt

@@ -0,0 +1,11 @@
+// <<< smartCastsWithDestructuring.txt
+interface I1
+interface I2
+
+operator fun I1.component1() = 1
+operator fun I2.component2() = ""
+
+fun test(x: I1) {
+    if (x !is I2) return
+    val (c1, c2) = x
+}