RFR: 8298048: Combine CDS archive heap into a single block

[Matias Saavedra Silva]

On Mon, 3 Apr 2023 03:32:27 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> This PR combines the "open" and "closed" regions of the CDS archive heap into a single region. This significantly simplifies the implementation, making it more compatible with non-G1 collectors. There's a net removal of ~1000 lines in src code and another ~1200 lines of tests.
> 
> **Notes for reviewers:**
> - Most of the code changes in CDS are removing the handling of "open" vs "closed" objects.
>   - Reviewers can start with ArchiveHeapWriter::copy_source_objs_to_buffer().
>   - It might be easier to see the diff with whitespaces off.
> - There are two major changes in the G1 code
>   - The archived objects are now stored in the "old" region (see g1CollectedHeap.cpp in [58d720e](https://github.com/openjdk/jdk/pull/13284/commits/58d720e294bb36f21cb88cddde724ed2b9e93770))
>   - The majority of the other changes are removal of the "archive" region type (see heapRegionType.hpp). For ease of review, such code is isolated in [a852dfb](https://github.com/openjdk/jdk/pull/13284/commits/a852dfbbf5ff56e035399f7cc3704f29e76697f6)
> - Testing changes:
>   - Now the archived java objects can move, along with the "old" regions that contain them. It's no longer possible to test whether a heap object came from CDS. As a result, the `WhiteBox.isShared(Object o)` API has been removed.
>   - Many tests that uses this API are removed. Most of them were written during early development of CDS archived objects and are no longer relevant.
> 
> **Testing:**
> - Mach5 tiers 1 ~ 7

Great cleanup! Making CDS easier to read and use is always a plus. Just some observations/nits:

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PR Comment: https://git.openjdk.org/jdk/pull/13284#issuecomment-1500569237