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.java

@@ -0,0 +1,57 @@
+package test;
+
+public abstract class C extends B implements I {
+    private final int mySomething1;
+    private int mySomething6;
+
+    C(int something1) {
+        mySomething1 = something1;
+    }
+
+    @Override
+    public int getSomething1() {
+        return mySomething1;
+    }
+
+    @Override
+    public int getSomething2() {
+        return 0;
+    }
+
+    @Override
+    public int getSomething3() {
+        return 0;
+    }
+
+    @Override
+    public void setSomething3(int value) {
+    }
+
+    @Override
+    public int getSomething4() {
+        return 0;
+    }
+
+    @Override
+    public void setSomething5(int value) {
+
+    }
+
+    public int getSomething6() {
+        return mySomething6;
+    }
+
+    @Override
+    public void setSomething6(int value) {
+        mySomething6 = value;
+    }
+
+    public String getFromB5() {
+        return "";
+    }
+
+    @Override
+    public void setFromB5(String value) {
+        super.setFromB5(value);
+    }
+}