use data flow info in constraint system

intersect data flow value possible types
add intersection type (or exact type for the most cases) as a lower bound to constraint system

always get common super type for intersection type as a result
(avoid returning it, even in error messages)

compiler/testData/diagnostics/tests/smartCasts/inference/kt1355.kt

@@ -0,0 +1,40 @@
+//KT-1355 Type inference fails with autocast and generic function
+//tests for Map.set
+package a
+
+import java.util.HashMap
+
+fun foo(map: MutableMap<Int, String>, value: String?) {
+    if (value != null) {
+        map.put(1, value) //ok
+        map.set(1, value) //type inference failed
+        map[1] = value    //type inference failed
+    }
+}
+
+//---------------------------
+
+public data open class Tag(public var tagName: String) {
+    public val attributes: MutableMap<String, String> = HashMap<String, String>()
+    public val contents: MutableList<Tag> = arrayListOf()
+
+    public var id: String?
+        get() = attributes["id"]
+        set(value) {
+            if(value == null) {
+                attributes.remove("id")
+            }
+            else {
+                attributes["id"] = value<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>
+                attributes["id"] = value
+            }
+        }
+}
+
+
+//from library
+fun <K, V> MutableMap<K, V>.set(key : K, value : V) = this.put(key, value)
+
+fun arrayListOf<T>(vararg <!UNUSED_PARAMETER!>values<!>: T): MutableList<T> = throw Exception()
+
+