RFR: 8374789: C2: refactor GraphKit code that create AddP nodes for raw memory to use helper method

[Guanqiang Han]

This PR refactors GraphKit code that creates AddP nodes for raw memory to use a dedicated helper method. This avoids passing top() explicitly at call sites and improves readability.

Please review this change. Thanks!

**Test:** GHA

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

Commit messages:
 - update copyright year
 - Merge remote-tracking branch 'upstream/master' into 8374789
 - Use off_heap_plus_addr for raw AddP address computation
 - Add helper for creating raw AddP nodes

Changes: https://git.openjdk.org/jdk/pull/29666/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29666&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374789
  Stats: 107 lines in 17 files changed: 21 ins; 3 del; 83 mod
  Patch: https://git.openjdk.org/jdk/pull/29666.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29666/head:pull/29666

PR: https://git.openjdk.org/jdk/pull/29666