Java to Kotlin converter: generate "!!." instead of "?." for nullable values

#KT-3943 Fixed

j2k/tests/testData/ast/annotations/jetbrainsNotNull.kt

@@ -6,7 +6,7 @@ public class Test(str: String) {
     var myStr: String = "String2"
 
     public fun sout(str: String) {
-        System.out?.println(str)
+        System.out!!.println(str)
     }
 
     public fun dummy(str: String): String {

j2k/tests/testData/ast/annotations/jetbrainsNotNullChainExpr.kt

@@ -15,8 +15,8 @@ class Bar() {
 class Test() {
     public fun test(barNotNull: Bar, barNullable: Bar?) {
         barNotNull.fooNotNull.execute()
-        barNotNull.fooNullable?.execute()
-        barNullable?.fooNotNull?.execute()
-        barNullable?.fooNullable?.execute()
+        barNotNull.fooNullable!!.execute()
+        barNullable!!.fooNotNull.execute()
+        barNullable!!.fooNullable!!.execute()
     }
 }