RFR: 8377011: Shenandoah: assert_bounds should be only called when boundaries have changed [v3]

[Xiaolong Peng]

> This fix the problem causing following 3 jtreg tests with tlab disabled to fail:
> 
> gc/shenandoah/TestRetainObjects.java#no-tlab 8361099 generic-all
> gc/shenandoah/TestSieveObjects.java#no-tlab 8361099 generic-all
> gc/shenandoah/TestSieveObjects.java#no-tlab-genshen 8361099 generic-all
> 
> 
> 
> The problem is assert_bounds is always called from function ShenandoahFreeSet::try_allocate_in, no matter the boundaries have changed or not after the allocation,  this is new behavior introduced by https://bugs.openjdk.org/browse/JDK-8365880, before which assert_bounds was only called after retiring a region.
> 
> The fix is to call assert_bounds only when boundaries have changed:
> 1. When retire a region;
> 2. When a the object is allocated in a new region - one region became non-empty.
> 
> There is also minor improvement to the if-else code in the PR.
> 
> Overall the change should be safe and only affect Shenandoah related tests, I have run Shenandoah test suite on MacOS.
> 
> Profiler data from the problematic jtreg test: [jtreg-gc_shenandoah_TestRetainObjects_no_tlab.html](https://github.com/user-attachments/files/25027324/jtreg-gc_shenandoah_TestRetainObjects_no_tlab.html) 
> 
> ### Tests
> - [x] hotspot_gc_shenandoah
> - [x] GHA

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

  code format

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29537/files
  - new: https://git.openjdk.org/jdk/pull/29537/files/ea68047f..4339e8c5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29537&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29537&range=01-02

  Stats: 10 lines in 1 file changed: 4 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/29537.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29537/head:pull/29537

PR: https://git.openjdk.org/jdk/pull/29537