RFR: 8276790: Rename GenericCDSFileMapHeader::_base_archive_path_offset

[Ioi Lam]

Please review this trivial change that improves consistency in the source code:

In the `GenericCDSFileMapHeader` structure, rename


_base_archive_path_offset => _base_archive_name_offset


I also changed the names used by various tests accordingly.

Running tiers 1-4

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Commit messages:
 - 8276790: Rename GenericCDSFileMapHeader::_base_archive_path_offset

Changes: https://git.openjdk.java.net/jdk/pull/6288/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6288&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276790
  Stats: 60 lines in 7 files changed: 0 ins; 0 del; 60 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6288.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6288/head:pull/6288

PR: https://git.openjdk.java.net/jdk/pull/6288