RFR: 8273508: Support archived heap objects in SerialGC [v2]

[Ioi Lam]

> When `-XX:+UseSerialGC is enabled`, load the CDS archived heap objects into `SerialHeap::old_gen()` during VM bootstrap. This improves VM start-up time, mostly because the module graph can be loaded from the archive.
> 
> 
> $ perf stat -r 40 java -XX:+UseSerialGC -version
> 
> Before: 0.042484507 seconds time elapsed ( +- 0.72% )
> After:  0.031671000 seconds time elapsed ( +- 0.72% )
> 
> 
> Changes in the gc subdirectories are contributed by @tschatzl

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

  @tschatzl comments

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5596/files
  - new: https://git.openjdk.java.net/jdk/pull/5596/files/9027660e..7d841aae

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5596&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5596&range=00-01

  Stats: 7 lines in 2 files changed: 1 ins; 3 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5596.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5596/head:pull/5596

PR: https://git.openjdk.java.net/jdk/pull/5596