StreamApiMigrationInspection: use collect when computeIfAbsent is used; VariableAccessUtils#variableIsUsed instead of ReferenceSearch (IDEA-CR-16490)

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

@@ -0,0 +1,11 @@
+// "Replace with collect" "true"
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+public class Main {
+  private Map<Integer, List<String>> test(String... list) {
+      Map<Integer, List<String>> map = Arrays.stream(list).collect(Collectors.groupingBy(String::length));
+      return map;
+  }
+}

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

@@ -0,0 +1,13 @@
+// "Replace with collect" "true"
+
+import java.util.*;
+
+public class Main {
+  private Map<Integer, List<String>> test(String... list) {
+    Map<Integer, List<String>> map = new HashMap<>();
+    for(String s : l<caret>ist) {
+      map.computeIfAbsent(s.length(), k -> new ArrayList<>()).add(s);
+    }
+    return map;
+  }
+}