RFR: 8273152: Store base archive path in CDSFileMapHeaderBase [v2]

[Yumin Qi]

> Store base archive path offset in CDSFileMapHeaderBase (which should be invariant in evolving versions) so we can read the base archive name reliably from dynamic archive even with variant header sizes over versions.
> 
> tests: tier1-4
> 
> Thanks
> Yumin

Yumin Qi has updated the pull request incrementally with two additional commits since the last revision:

 - Fixed typo
 - Moved _header_size from FileMapHeader to CDSFileMapHeaderBase and added tests

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5584/files
  - new: https://git.openjdk.java.net/jdk/pull/5584/files/2877aa61..d82587fb

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5584&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5584&range=00-01

  Stats: 145 lines in 8 files changed: 106 ins; 3 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5584.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5584/head:pull/5584

PR: https://git.openjdk.java.net/jdk/pull/5584