New J2K: make post-processing aware of other files which are being converted

Before post-processing was able to handle only one converting file at once
So, some conversions (like (field, getter, setter) to Kotlin property)
was not able to work when converting class hierarchy was split into
multiple files.
Also, inferring nullability for a set of files was broken

#KT-19569 fixed
#KT-34266 fixed
#KT-32518 fixed

nj2k/testData/multiFile/DetectPropertiesMultipleFiles/C.kt

@@ -0,0 +1,34 @@
+package test
+
+abstract class C internal constructor(override val something1: Int) : B(), I {
+    private var mySomething6 = 0
+
+    override val something2: Int
+        get() = 0
+
+    override var something3: Int
+        get() = 0
+        set(value) {}
+
+    override fun getSomething4(): Int {
+        return 0
+    }
+
+    override fun setSomething5(value: Int) {}
+    fun getSomething6(): Int {
+        return mySomething6
+    }
+
+    override fun setSomething6(value: Int) {
+        mySomething6 = value
+    }
+
+    fun getFromB5(): String {
+        return ""
+    }
+
+    override fun setFromB5(value: String?) {
+        super.setFromB5(value)
+    }
+
+}