RFR: 8357286: (bf) Remove obsolete instanceof checks in CharBuffer.append [v2]

[Alan Bateman]

On Wed, 11 Jun 2025 22:36:49 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Remove some instanceof checks which are vestigial now that `CharSequence` itself defines `getChars(int,int,char[],int)`.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8357286: Correctly handle null CharSequence

Updated patch looks okay, I assume at least tier1-3 have been run with the changes.

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Marked as reviewed by alanb (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25739#pullrequestreview-2919735334