RFR: 8371381: [Shenandoah] Setting ergo flags should use FLAG_SET_ERGO [v2]

[Rui Li]

> Setting ergo flags using `FLAG_SET_ERGO`, instead of `FLAG_SET_DEFAULT`, so we can have the right origin info.
> 
> Had to expand `ShenandoahEvacReserve` range from `range(1,100)` to `range(0,100)` because when we use shenandoah passive mode and degen is also turned off (`-XX:ShenandoahGCMode=passive -XX:-ShenandoahDegeneratedGC`), we set the ShenandoahEvacReserve to 0:  https://github.com/openjdk/jdk/blob/c6a8027b94bbcbde5f7dcabd0bff48b93bbb5a7f/src/hotspot/share/gc/shenandoah/mode/shenandoahPassiveMode.cpp#L41 The issue is surfaced now because `FLAG_SET_DEFAULT` doesn't check the range but `FLAG_SET_ERGO` does.
> 
> Testing: jtreg gc. GHA pending.

Rui Li has updated the pull request incrementally with one additional commit since the last revision:

  Use FLAG_SET_DEFAULT for ShenandoahEvacReserve in passive

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28242/files
  - new: https://git.openjdk.org/jdk/pull/28242/files/1a5a09bf..65fc9878

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28242&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28242&range=00-01

  Stats: 8 lines in 2 files changed: 4 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/28242.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28242/head:pull/28242

PR: https://git.openjdk.org/jdk/pull/28242