Filtering error types and accounting for platform types when computing intersections

KT-6508 Build impossible because of NoSuchElementException

 #KT-6508 Fixed

compiler/testData/diagnostics/tests/platformTypes/intersection/map.kt

@@ -0,0 +1,11 @@
+// !EXPLICIT_FLEXIBLE_TYPES
+
+fun foo(
+        p1: ft<MutableMap<Int, String>, Map<Int, String>?>,
+        p2: Map<Int, String>
+) = p1 == p2
+
+fun foo(
+        p1: ft<String, String?>,
+        p2: String
+) = p1 == p2

compiler/testData/diagnostics/tests/platformTypes/intersection/map.txt

@@ -0,0 +1,4 @@
+package
+
+internal fun foo(/*0*/ p1: kotlin.(Mutable)Map<kotlin.Int, kotlin.String>!, /*1*/ p2: kotlin.Map<kotlin.Int, kotlin.String>): kotlin.Boolean
+internal fun foo(/*0*/ p1: kotlin.String!, /*1*/ p2: kotlin.String): kotlin.Boolean

compiler/testData/diagnostics/tests/regressions/kt6508.kt

@@ -0,0 +1,24 @@
+// !DIAGNOSTICS: -UNUSED_EXPRESSION
+
+// FILE: foo/View.java
+
+package foo;
+
+public class View {}
+
+// FILE: foo/TextView.java
+
+package foo;
+
+public class TextView extends View {}
+
+// FILE: k.kt
+
+import foo.View
+//import foo.TextView
+
+fun String.gah(view:View ?) {
+    if (view is <!UNRESOLVED_REFERENCE!>TextView<!>)
+        <!DEBUG_INFO_SMARTCAST!>view<!>
+    else <!UNRESOLVED_REFERENCE!>TextView<!>() as foo.TextView
+}

compiler/testData/diagnostics/tests/regressions/kt6508.txt

@@ -0,0 +1,3 @@
+package
+
+internal fun kotlin.String.gah(/*0*/ view: foo.View?): kotlin.Unit