RFR: 8351443: Improve robustness of StringBuilder

[Hendrik Schick]

On Wed, 30 Apr 2025 14:12:36 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> Refactor AbstractStringBuilder to maintain consistency among count, coder, and value buffers while the buffer capacity is being expanded and/or inflated from Latin1 to UTF16 representations. 
> The refactoring pattern is to read and write AbstractStringBuilder fields once using locals for all intermediate values. 
> Support methods are static, designed to pass all values as arguments and return a value.
> 
> The value byte array is reallocated under 3 conditions:
> - Increasing the capacity with the same encoder
> - Increasing the capacity and inflation to change the coder from LATIN1 to UTF16
> - Inflation with the same capacity
> 
> Added StressSBTest to exercise public instance methods of StringBuilder.

test/jdk/java/lang/StringBuilder/StringBuilderRepeat.java line 110:

> 108:         String expected = "repeat233333233333-2-3-3-3-3-3\u2461\u2462\u2462\u2462\u2462\u2462\u2461\u2462\u2462\u2462\u2462\u2462-\u2461-\u2462-\u2462-\u2462-\u2462-\u2462abcabcabc" +
> 109:                           "nullnullnullnullnullnullnullnullnullnullnullnull";
> 110:         assertEquals(expected, sb.toString());

copyright year update missing

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PR Review Comment: https://git.openjdk.org/jdk/pull/24967#discussion_r2070317617