RFR: 8268164: Adopt cast notation for WorkerThread conversions [v2]

[Albert Mingkun Yang]

> Followup of JDK-8267916 (#4240), the same refactoring for `WorkerThread`.

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  review

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4334/files
  - new: https://git.openjdk.java.net/jdk/pull/4334/files/aa2769f4..daf5990f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4334&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4334&range=00-01

  Stats: 5 lines in 2 files changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4334.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4334/head:pull/4334

PR: https://git.openjdk.java.net/jdk/pull/4334