RFR: 8252661: Change SafepointMechanism terminology to talk less about "blocking"

[Erik Österlund]

Migrating this review from the mailing list into a pull request. So far, the favourite terminology is to talk about
"process", but without "operation".

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Commit messages:
 - 8252661: Change SafepointMechanism terminology to talk less about "blocking"

Changes: https://git.openjdk.java.net/jdk/pull/54/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=54&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252661
  Stats: 33 lines in 12 files changed: 0 ins; 0 del; 33 mod
  Patch: https://git.openjdk.java.net/jdk/pull/54.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/54/head:pull/54

PR: https://git.openjdk.java.net/jdk/pull/54