RFR: 8335059: Consider renaming ClassLoaderData::keep_alive

[Coleen Phillimore]

How does this rename look?  Instead of ClassLoaderData::keep_alive() and a _keep_alive refcount, it's been renamed to _strongly_reachable and is_strongly_reachable().
Tested with tier1 on Oracle supported platforms.

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Commit messages:
 - Fix indent.
 - 8335059: Consider renaming ClassLoaderData::keep_alive

Changes: https://git.openjdk.org/jdk/pull/20408/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20408&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335059
  Stats: 37 lines in 10 files changed: 2 ins; 0 del; 35 mod
  Patch: https://git.openjdk.org/jdk/pull/20408.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20408/head:pull/20408

PR: https://git.openjdk.org/jdk/pull/20408