RFR: 8365814: Consolidate has_been_archived() and has_been_buffered() in ArchiveBuilder

[Ioi Lam]

Merged the two methods into one: `ArchiveBuilder::has_been_archived()`. Added comments and asserts to explain what the expected result is.

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Commit messages:
 - 8365814: Consolidate has_been_archived() and has_been_buffered() in ArchiveBuilder

Changes: https://git.openjdk.org/jdk/pull/26853/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26853&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365814
  Stats: 36 lines in 4 files changed: 20 ins; 10 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/26853.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26853/head:pull/26853

PR: https://git.openjdk.org/jdk/pull/26853