RemoveUnusedVariableUtil: code generation fixes

1. Support Java 12 switch rules and switch expressions (IDEA-203692)
2. Support void expression lambdas
3. Fix PSI structure when expression list statement is reduced to single expression

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/removeUnusedVariable/afterInCall.java

@@ -0,0 +1,6 @@
+// "Remove variable 'i'" "true"
+public class Main {
+  void test(String s) {
+      foo(1);
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/removeUnusedVariable/afterInVoidLambda.java

@@ -0,0 +1,8 @@
+// "Remove field 'x'" "true"
+public class Main {
+
+    void test() {
+    Runnable r = () -> {
+    };
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/removeUnusedVariable/afterSwitchExprJava12Preview.java

@@ -0,0 +1,8 @@
+// "Remove variable 'i'" "true"
+public class Main {
+  int test(String s) {
+      return switch(s) {
+      default -> 1;
+    }
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/removeUnusedVariable/afterSwitchJava12Preview.java

@@ -0,0 +1,9 @@
+// "Remove variable 'i'" "true"
+public class Main {
+  void test(String s) {
+      switch(s) {
+      case "foo" -> {
+      }
+    }
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/removeUnusedVariable/beforeInCall.java

@@ -0,0 +1,7 @@
+// "Remove variable 'i'" "true"
+public class Main {
+  void test(String s) {
+    int <caret>i;
+    foo(i = 1);
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/removeUnusedVariable/beforeInVoidLambda.java

@@ -0,0 +1,8 @@
+// "Remove field 'x'" "true"
+public class Main {
+  private int <caret>x;
+
+  void test() {
+    Runnable r = () -> x = 1;
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/removeUnusedVariable/beforeSwitchExprJava12Preview.java

@@ -0,0 +1,9 @@
+// "Remove variable 'i'" "true"
+public class Main {
+  int test(String s) {
+    int <caret>i;
+    return switch(s) {
+      default -> i = 1;
+    }
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/removeUnusedVariable/beforeSwitchJava12Preview.java

@@ -0,0 +1,9 @@
+// "Remove variable 'i'" "true"
+public class Main {
+  void test(String s) {
+    int <caret>i;
+    switch(s) {
+      case "foo" -> i = 1;
+    }
+  }
+}