RFR: 8366057: HotSpot Style Guide should permit trailing return types

[Kim Barrett]

Please review this change to the HotSpot Style Guide to permit trailing return
types for functions.

This is a modification of the Style Guide, so rough consensus among the
HotSpot Group members is required to make this change. Only Group members
should vote for approval (via the github PR), though reasoned objections or
comments from anyone will be considered. A decision on this proposal will not
be made before Monday 8-September-2025 at 12h00 UTC.

Since we're piggybacking on github PRs here, please use the PR review process
to approve (click on Review Changes > Approve), rather than sending a "vote:
yes" email reply that would be normal for a CFV.

-------------

Commit messages:
 - permit trailing return types

Changes: https://git.openjdk.org/jdk/pull/26923/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26923&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366057
  Stats: 89 lines in 2 files changed: 80 ins; 5 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/26923.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26923/head:pull/26923

PR: https://git.openjdk.org/jdk/pull/26923