Avoid magic `OutputFormat` method forwarding

[oliverklee]

• src/CSSList/AtRuleBlockList.php
• src/CSSList/CSSList.php
• src/CSSList/Document.php
• src/CSSList/KeyFrame.php
• src/Property/Charset.php
• src/Property/Import.php
• src/Rule/Rule.php
• src/RuleSet/AtRuleSet.php
• src/RuleSet/DeclarationBlock.php
• src/RuleSet/RuleSet.php
• src/Value/CalcRuleValueList.php
• src/Value/Color.php
• src/Value/ValueList.php