IDEA-167088 Stream API migration: allow resulting StringBuilder usages in concatenation

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/afterJoiningConcat.java

@@ -0,0 +1,16 @@
+// "Replace with collect" "true"
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class Test {
+  static String test(List<String> list) {
+    String sb;
+    System.out.println("hello");
+      sb = list.stream().filter(s -> !s.isEmpty()).map(String::trim).collect(Collectors.joining());
+    String s = "Result: ";
+    s += sb;
+    System.out.println(s);
+    return "[" + sb + "]";
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/beforeJoiningConcat.java

@@ -0,0 +1,19 @@
+// "Replace with collect" "true"
+
+import java.util.List;
+
+public class Test {
+  static String test(List<String> list) {
+    StringBuilder sb = new StringBuilder();
+    System.out.println("hello");
+    for(String s : li<caret>st) {
+      if(!s.isEmpty()) {
+        sb.append(s.trim());
+      }
+    }
+    String s = "Result: ";
+    s += sb;
+    System.out.println(s);
+    return "[" + sb + "]";
+  }
+}