RFR: 8250989: Consolidate buffer allocation code for CDS static/dynamic dumping [v3]

[Ioi Lam]

> Before this PR, when a static CDS archive is dumped, we would unconditionally allocate a 4GB ReservedSpace and use that as the buffer for writing the archive content. We usually don't need such a big ReservedSpace. this also unnecessarily complicates Metaspace::global_initialize().
> 
> After this PR, both we first load all the classes and then allocate a buffer with an appropriate size.
> 
> I also simplified the pointer relocation code that prepares the archive to be mapped at the "requested location" (usually 0x800000000), and improved the comments.
> 
> We used to have lots of special cases for adjusting pointers during dynamic dump. All of those are removed.
> 
> Reviewers, please start with
> - Header comments in archiveBuilder.hpp that describe the overall process of archive dumping
> - `MetaspaceShared::initialize_for_static_dump()`
> - `ArchiveBuilder::reserve_buffer()`
> - Comments around `RelocateBufferToRequested` in archiveBuilder.cpp

Ioi Lam has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:

 - @coleenp and @tstuefe comments
 - Merge branch 'master' into 8250989-consolidate-dump-buffer-alloc
 - @calvinccheung and @tstuefe comments
 - fixed whitespace
 - clean up and comments
 - move remaining functions to archiveBuilder.cpp
 - renamed "default" to "requested"
 - started

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2296/files
  - new: https://git.openjdk.java.net/jdk/pull/2296/files/eac50351..aa4079bb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2296&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2296&range=01-02

  Stats: 30463 lines in 903 files changed: 11819 ins; 7876 del; 10768 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2296.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2296/head:pull/2296

PR: https://git.openjdk.java.net/jdk/pull/2296