RFR: 8373056: Shenandoah: Remove unnecessary use of ShenandoahAllocRequest.type() [v3]

[Xiaolong Peng]

> Follow up on the feedback/comments on PR https://github.com/openjdk/jdk/pull/28521 for bug [JDK-8372566](https://bugs.openjdk.org/browse/JDK-8372566), we should avoid using ShenandoahAllocRequest.type() directly if possible, in most of cases we don't need to directly use alloc type, the inline member methods provided by ShenandoahAllocRequest should be sufficient.
> 
> In the PR, I have removed most of the places where ShenandoahAllocRequest.type() directly used, there will be only one place left after the change:
> * ShenandoahFreeSet::allocate (This one will be removed with PR https://github.com/openjdk/jdk/pull/26171)
> 
> Also did small code rearrangement for ShenandoahOldGeneration::configure_plab_for_current_thread 
> 
> ### Test
> - [x] hotspot_gc_shenandoah
> - [ ] GHA

Xiaolong Peng has updated the pull request incrementally with one additional commit since the last revision:

  Remove outdated comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28649/files
  - new: https://git.openjdk.org/jdk/pull/28649/files/59087c8e..57305932

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28649&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28649&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28649.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28649/head:pull/28649

PR: https://git.openjdk.org/jdk/pull/28649