Improve quickfix to replace += operator with StringBuilder on left hand side with append() call

now works on java.lang.Appendable and splits concatenated strings into separate append calls

java/java-tests/testSrc/com/intellij/codeInsight/daemon/quickFix/ChangeToAppendTest.java

@@ -0,0 +1,11 @@
+package com.intellij.codeInsight.daemon.quickFix;
+
+public class ChangeToAppendTest extends LightQuickFixTestCase {
+
+  public void test() throws Exception { doAllTests(); }
+
+  @Override
+  protected String getBasePath() {
+    return "/codeInsight/daemonCodeAnalyzer/quickFix/changeToAppend";
+  }
+}