RFR: 8374789: C2: refactor GraphKit code that create AddP nodes for raw memory to use helper method [v8]

[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

Guanqiang Han has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 15 additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into 8374789
 - Merge two lines into one
 - Adjust code style again
 - Adjust code style
 - Merge remote-tracking branch 'upstream/master' into 8374789
 - adjust code style
 - adjust code style
 - Merge remote-tracking branch 'upstream/master' into 8374789
 - Align properly
 - Replace AddPNode constructor calls with static func
 - ... and 5 more: https://git.openjdk.org/jdk/compare/d4297279...3d07f2fe

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29666/files
  - new: https://git.openjdk.org/jdk/pull/29666/files/e1123557..3d07f2fe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29666&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29666&range=06-07

  Stats: 86636 lines in 399 files changed: 36734 ins; 35702 del; 14200 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