RFR: 8351443: Improve robustness of StringBuilder [v2]

[Roger Riggs]

> 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.

Roger Riggs has updated the pull request incrementally with one additional commit since the last revision:

  Added missing bugid to tests
  Applied review suggestions.
  Added convenience methods to StringLatin1 for 4 and 5 character literals to leverage optimizations for merged stores.
  Updated missing copyright years.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24967/files
  - new: https://git.openjdk.org/jdk/pull/24967/files/b59a2e9a..f5003244

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24967&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24967&range=00-01

  Stats: 55 lines in 6 files changed: 16 ins; 14 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/24967.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24967/head:pull/24967

PR: https://git.openjdk.org/jdk/pull/24967