RFR: 8273508: Support archived heap objects in SerialGC

[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

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Commit messages:
 - 8273508: Support archived heap objects in SerialGC

Changes: https://git.openjdk.java.net/jdk/pull/5596/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5596&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273508
  Stats: 211 lines in 12 files changed: 179 ins; 1 del; 31 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