New J2K: split diagnostic based processing from inspection ones

Analysing file file with diagnostics on each step of post-processings is rather expensive operation so the inspection-like post-processings which don't require diagnostic information was separated from ones that need it

Related to #KT-31848

nj2k/testData/newJ2k/issues/kt-794.kt

@@ -1,4 +1,7 @@
 internal class Test {
     val int: Int
-        get() = 10
+        get() {
+            val b: Byte = 10
+            return b.toInt()
+        }
 }

nj2k/testData/newJ2k/postProcessing/RedundantTypeCastAndInline.kt

@@ -1,8 +1,9 @@
 internal class C {
     fun foo(o: Any?) {
         if (o is String) {
-            val l = o.length
-            val substring = o.substring(l - 2)
+            val s = o
+            val l = s.length
+            val substring = s.substring(l - 2)
         }
     }
 }