Improve fixes for StatementSwitchToExpressionSwitch

[copybara-service]

Improve fixes for StatementSwitchToExpressionSwitch

If a case contains a single block statement, skip past the braces of the block statement.

Enables fixes like:

      case 0 -> System.out.println("0");

Instead of:

      case 0 -> {
        {
          System.out.println("0");
          break;
        }
      }

Fixes #4222