RFR: JDK-8280594: Refactor annotation invocation handler handling to use Objects.toIdentityString

[Joe Darcy]

Simple refactoring to use new-in19 library code.

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

Commit messages:
 - JDK-8280594: Refactor annotation invocation handler handling to use Objects.toIdentityString

Changes: https://git.openjdk.java.net/jdk/pull/8310/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8310&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280594
  Stats: 10 lines in 1 file changed: 0 ins; 9 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8310.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8310/head:pull/8310

PR: https://git.openjdk.java.net/jdk/pull/8310