RFR: 8372040: Remove Prefetch header vs inline header separation

[jonghoonpark]

related jira issue: https://bugs.openjdk.org/browse/JDK-8372040

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## Changes

- Merged `prefetch.hpp` into `prefetch.inline.hpp` and removed the redundant `prefetch.hpp`. Updated all call sites accordingly.
- Removed `runtime/prefetch.inline.hpp` from `generation.hpp` to adhere to the rule that standard headers should not include inline headers.
    - Added the inclusion of `runtime/prefetch.inline.hpp` to `cardTableRS.cpp` instead.
- Removed `runtime/prefetch.hpp` from `g1YoungGCPostEvacuateTasks.cpp` as it is already included via `g1HeapRegion.inline.hpp`.

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Verified with tier1 testing; no regressions found.

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Commit messages:
 - Merge prefetch.hpp into prefetch.inline.hpp and cleanup dependencies

Changes: https://git.openjdk.org/jdk/pull/29096/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29096&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372040
  Stats: 103 lines in 18 files changed: 17 ins; 68 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/29096.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29096/head:pull/29096

PR: https://git.openjdk.org/jdk/pull/29096