RFR: 8361209: (bf) Use CharSequence::getChars for StringCharBuffer bulk get methods [v5]

[Brian Burkhalter]

On Wed, 16 Jul 2025 23:23:30 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> For `CharBuffer`s created from a `CharSequence`, use `CharSequence.getChars` to perform bulk gets instead of successively copying single characters.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8361209: Fix assertion added in previous commit

The change in this request passed several hundred repetitions of the new test proposed in #26282.

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PR Comment: https://git.openjdk.org/jdk/pull/26251#issuecomment-3103764941