RFR: 8338888: SystemDictionary::class_name_symbol has incorrect length check

[David Holmes]

The name length check was incorrectly truncating the length to an int, which is wrong if the name is > `INT_MAX`. Added a test for this case to the existing test cases and fixed an issue with the call to `Exceptions::fthrow` that can hit the `INT_MAX` limitations of `os::vsnprintf` (this is the first in a serious of fixes that will mainly be done under [JDK-8328882](https://bugs.openjdk.org/browse/JDK-8328882) or subtasks thereof).

Testing:
 - updated test
 - tiers 1-3 (sanity)

Thanks

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Commit messages:
 - whitespace
 - Refactor to share code
 - 8338888: SystemDictionary::class_name_symbol has incorrect length check

Changes: https://git.openjdk.org/jdk/pull/20709/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20709&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338888
  Stats: 82 lines in 3 files changed: 71 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/20709.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20709/head:pull/20709

PR: https://git.openjdk.org/jdk/pull/20709