Java inspection: simplified "Make Type Generic" inspection's visitor, test added (IDEA-157727)

java/java-tests/testData/codeInspection/makeTypeGeneric/AtEquals.java

@@ -0,0 +1,5 @@
+import java.util.*;
+
+public class F {
+  List list <caret>= new ArrayList<String>();
+}

java/java-tests/testData/codeInspection/makeTypeGeneric/AtEquals_after.java

@@ -0,0 +1,5 @@
+import java.util.*;
+
+public class F {
+  List<String> list = new ArrayList<String>();
+}