RFR: 8296155: Simplify CDS heap region address calculation [v2]

[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`

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  @coleenp comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10923/files
  - new: https://git.openjdk.org/jdk/pull/10923/files/5cbbe3a5..06f85c9e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10923&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10923&range=00-01

  Stats: 5 lines in 2 files changed: 3 ins; 0 del; 2 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