RFR: 8288537: Move Devirtualizer out of hotspot/share/memory/iterator.hpp [v4]

[Ioi Lam]

> HotSpot build time has regressed quite a bit since JDK 17 (1m46s vs 2m20s on my machine). Now it's time to do some header file cleanup.
> 
> iterator.hpp contains a hodge-podge of unrelated classes. Some of these classes have dependencies on other headers (e.g., `Devirtualizer` depends on bitMap.hpp) that slow down C++ compilation.
> 
> This patch moves two infrequently used classes, `Devirtualizer` and `SerializeClosure`, to their own header files. This reduces the total number of C++ lines compiled for libjvm.so for about 1%.

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

  Updated copyright year to 2018, where the Devirtualizer class was first added

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9176/files
  - new: https://git.openjdk.org/jdk/pull/9176/files/ba07ef2c..ab986620

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9176&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9176&range=02-03

  Stats: 5 lines in 2 files changed: 2 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/9176.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9176/head:pull/9176

PR: https://git.openjdk.org/jdk/pull/9176