RFR: 8364212: Shenandoah: Rework archived objects loading [v2]

[Aleksey Shipilev]

> As continuation of [JDK-8293650](https://bugs.openjdk.org/browse/JDK-8293650), we would want to avoid allocating CDS archives as humongous regions and then flipping them back to regular state. This already complicates the region accounting significantly, and was a source a few bugs. We can rework the CDS archive load to cleanly ask collector for a contiguous set of regular regions.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`
>  - [x] Linux x86_64 server fastdebug, `runtime/cds`
>  - [x] Linux x86_64 server fastdebug, `runtime/cds` with `-XX:+UseShenandoahGC`
>  - [ ] Linux x86_64 server fastdebug, `all`

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  A bit more verification

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26510/files
  - new: https://git.openjdk.org/jdk/pull/26510/files/7795c570..dcd8e3e7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26510&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26510&range=00-01

  Stats: 15 lines in 1 file changed: 8 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/26510.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26510/head:pull/26510

PR: https://git.openjdk.org/jdk/pull/26510