RFR: 8074101: Add verification that all tasks are actually claimed during roots processing [v3]

[Albert Mingkun Yang]

> The first commit removes some obsolete enum items, while the second commit adds the verification logic. Commit 2 introduces some "empty" task claims for the verification logic, explicitly marked in the comments.
> 
> Test: hotspot_gc

Albert Mingkun Yang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  review

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2046/files
  - new: https://git.openjdk.java.net/jdk/pull/2046/files/938dce1d..aa2d853c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2046&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2046&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2046.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2046/head:pull/2046

PR: https://git.openjdk.java.net/jdk/pull/2046