New J2K: rearrange and optimize some post-processings

nj2k/testData/newJ2k/issues/kt-19336.kt

@@ -1,6 +1,6 @@
 class TestReturnsArray {
     fun strings(n: Int): Array<String?> {
-        val result: Array<String?> = arrayOfNulls(n)
+        val result = arrayOfNulls<String>(n)
         for (i in 0 until n) {
             result[i] = Integer.toString(i)
         }

nj2k/testData/newJ2k/issues/kt-19604.kt

@@ -1,7 +1,7 @@
 import java.util.HashMap
 
 class TestMethodReference {
-    private val hashMap: HashMap<String, String> = HashMap()
+    private val hashMap = HashMap<String, String>()
     fun update(key: String, msg: String) {
         hashMap.merge(key, msg) { obj: String, s: String -> obj + s }
     }

nj2k/testData/newJ2k/issues/kt-19606.kt

@@ -1,7 +1,7 @@
 import java.util.HashMap
 
 class TestMethodReference {
-    private val hashMap: HashMap<String, String> = HashMap()
+    private val hashMap = HashMap<String, String>()
     fun update(key: String, msg: String) {
         hashMap.merge(key, msg) { obj: String, s: String -> obj + s }
     }

nj2k/testData/newJ2k/issues/kt-8170.kt

@@ -2,12 +2,12 @@ object ArrayNullable {
     @JvmStatic
     fun main(args: Array<String>) {
         val notNull = 0
-        val a1: Array<Int?> = arrayOfNulls(2)
+        val a1 = arrayOfNulls<Int>(2)
         a1[0] = null
         a1[1] = notNull
         println(a1[0])
         println(a1[1])
-        val a2: Array<Int?> = arrayOfNulls(2)
+        val a2 = arrayOfNulls<Int>(2)
         a2[0] = nullable()
         a2[1] = notNull
         println(a2[0])