RFR: JDK-8304945: StringBuilder and StringBuffer should implement Appendable explicitly

[M4ximumPizza]

On Sat, 1 Apr 2023 17:34:37 GMT, Joe Darcy <darcy at openjdk.org> wrote:

> The StringBuilder and StringBuffer classes are Appendable by virtue of from subclasses their non-public superclass AbstractStringBuilder.
> 
> It is slightly clearer to declare StringBuilder and StringBuffer to directly implement Appendable, as they already directly implement the CharSequence interface also implemented by their superclass.
> 
> There are no other interfaces implemented by AbstractStringBuilder other than Appendable and CharSequence.
> 
> Please also review the CSR https://bugs.openjdk.org/browse/JDK-8305408

Marked as reviewed by M4ximumPizza at github.com (no known OpenJDK username).

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PR Review: https://git.openjdk.org/jdk/pull/13278#pullrequestreview-1368032789