Check nullability in initial constraints

except constraints for receiver type (it can be accessed via safe call)

compiler/testData/diagnostics/tests/inference/regressions/kt1127.kt

@@ -5,5 +5,5 @@ package d
 fun <T> asList(<!UNUSED_PARAMETER!>t<!>: T) : List<T>? {<!NO_RETURN_IN_FUNCTION_WITH_BLOCK_BODY!>}<!>
 
 fun main(args : Array<String>) {
-    val <!UNUSED_VARIABLE!>list<!> : List<String> = <!TYPE_MISMATCH!>asList("")<!>
+    val <!UNUSED_VARIABLE!>list<!> : List<String> = <!TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>asList("")<!>
 }

compiler/testData/diagnostics/tests/inference/regressions/kt2286.kt

@@ -11,14 +11,14 @@ abstract class Buggy {
     }
 
     val anotherThree : Int
-        get() = <!TYPE_MISMATCH!>coll.find{ it > 3 }<!> // does not work here
+        get() = coll.<!TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>find{ it > 3 }<!> // does not work here
 
     val yetAnotherThree : Int
-        get() = <!TYPE_MISMATCH!>coll.find({ v:Int -> v > 3 })<!> // neither here
+        get() = coll.<!TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>find({ v:Int -> v > 3 })<!> // neither here
 
     val extendedGetter : Int
         get() {
-            return <!TYPE_MISMATCH!>coll.find{ it > 3 }<!>  // not even here!
+            return coll.<!TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>find{ it > 3 }<!>  // not even here!
         }
 
 }

compiler/testData/diagnostics/tests/inference/regressions/kt2838.kt

@@ -7,7 +7,7 @@ fun <T> bar(a: T, b: Map<T, String>) = b.get(a)
 
 fun test(a: Int) {
     foo(a, null)
-    bar(a, <!NULL_FOR_NONNULL_TYPE!>null<!>)
+    <!TYPE_INFERENCE_INCORPORATION_ERROR!>bar<!>(a, <!NULL_FOR_NONNULL_TYPE!>null<!>)
 }
 fun test1(a: Int) {
     foo(a, throw Exception())