RFR: 8296155: Simplify CDS heap region address calculation

[Ioi Lam]

Rewrite and simplify the convoluted logic used to calculate the runtime location of a CDS heap region. Now it's as simple as:


FileMapRegion::dumptime_base() + ArchiveHeapLoader::runtime_delta();


See `FileMapInfo::heap_region_runtime_start_address` for an example.

Also removed dead code:

- `FileMapInfo::is_in_shared_region`
- `MetaspaceShared::is_in_shared_region`
- `FileMapInfo::stop_sharing_and_unmap`

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Commit messages:
 - 8296155: Simplify CDS heap region address calculation

Changes: https://git.openjdk.org/jdk/pull/10923/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10923&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296155
  Stats: 134 lines in 7 files changed: 20 ins; 97 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/10923.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10923/head:pull/10923

PR: https://git.openjdk.org/jdk/pull/10923