Added allowInSwitchCase property to AvoidNestedBlocksCheck

to allow limiting the scope of variables to one case of a switch statement.

src/testinputs/com/puppycrawl/tools/checkstyle/InputNestedBlocks.java

@@ -29,14 +29,33 @@ class InputNestedBlocks
             x = 2;
         }
 
+        // case statements are a bit complicated,
+        // they do not have its own variable scope by default.
+        // Hence it may be OK in some development teams to allow
+        // nested blocks if they are the complete case body.
         switch (x)
         {
             case 0:
-                x = 3; // OK
+                // OK
+                x = 3;
                 break;
+            case 1:
+                // Not OK, SLIST is not complete case body
+                {
+                    x = 1;
+                }
+                break;
+            case 2:
+                // OK if allowInSwitchCase is true, SLIST is complete case body
+                {
+                    x = 1;
+                    break;
+                }
+            case 3: // test fallthrough
             default:
-                {   // should be marked, even if a switch
-                    // case does not have its own scope
+                // Not OK, SLIST is not complete case body
+                System.out.println("Hello");
+                {
                     x = 2;
                 }
         }