RFR: 8265604: Support unlinked classes in dynamic CDS archive [v2]

[Calvin Cheung]

> This change adds the capability of storing unlinked class in dynamic CDS archive.
> Before this change, unlinked classes loaded by custom class loaders won't be store in dynamic CDS archive.
> Unlinked old classes with version < JAVA_6_VERSION will also be supported by this change. Similar to the support for old classes in static CDS archive in [JDK-8261090](https://bugs.openjdk.java.net/browse/JDK-8261090).
> 
> Testing:
> 
> - [x] tiers1,2,3,4

Calvin Cheung has updated the pull request incrementally with one additional commit since the last revision:

  @yminqi comments and add a new test

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4803/files
  - new: https://git.openjdk.java.net/jdk/pull/4803/files/2a8b1417..6a572478

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4803&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4803&range=00-01

  Stats: 138 lines in 4 files changed: 135 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4803.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4803/head:pull/4803

PR: https://git.openjdk.java.net/jdk/pull/4803