RFR: 8272520: Inline GenericTaskQueue::initialize() to the constructor

[Albert Mingkun Yang]

Simple refactoring of GenericTaskQueue initialization API.

Test: tier1_gc

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Commit messages:
 - ctor-init

Changes: https://git.openjdk.java.net/jdk/pull/5125/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5125&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272520
  Stats: 22 lines in 10 files changed: 1 ins; 20 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5125.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5125/head:pull/5125

PR: https://git.openjdk.java.net/jdk/pull/5125