RFR: 8375237: Document existing exceptional behavior of divideUnsigned and remainderUnsigned

[Joe Darcy]

Happened to notice the divideUnsigned and reminaderUnsigned methods don't document throwing ArithmeticException for a zero divisor so added I'm proposing to add the appropriate throws clauses.
The CSR is ready to review too.

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Commit messages:
 - 8375244: Document existing exceptional behavior of divideUnsigned and remainderUnsigned

Changes: https://git.openjdk.org/jdk/pull/29215/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29215&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375237
  Stats: 6 lines in 2 files changed: 4 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/29215.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29215/head:pull/29215

PR: https://git.openjdk.org/jdk/pull/29215