RFR: 8351462: Improve robustness of String concatenation

[Raffaello Giulietti]

Early detection of an `int` overflow in `StringConcatHelper` improves robustness of `StringConcatFactory`.

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Commit messages:
 - 8351462: Improve robustness of String concatenation

Changes: https://git.openjdk.org/jdk/pull/24546/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24546&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351462
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/24546.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24546/head:pull/24546

PR: https://git.openjdk.org/jdk/pull/24546