don't offer to replace with MessageFormat.format() when concatenation is constant (IDEA-18184 & IDEA-165981)

java/java-tests/testData/codeInsight/concatenationToMessageFormat/constant.java

@@ -0,0 +1,6 @@
+
+class Constant {
+  void f() {
+    String s = "a" + <caret>"b";
+  }
+}

java/java-tests/testData/codeInsight/concatenationToMessageFormat/simple.after.java

@@ -0,0 +1,6 @@
+class Simple {
+
+  void f(int i) {
+    String s = java.text.MessageFormat.format("a{0}b", i);
+  }
+}

java/java-tests/testData/codeInsight/concatenationToMessageFormat/simple.java

@@ -0,0 +1,6 @@
+class Simple {
+
+  void f(int i) {
+    String s = "a" + i + <caret>"b";
+  }
+}