RFR: 8268857: Merge VM_PrintJNI and VM_PrintThreads and remove the unused field 'is_deadlock' of DeadlockCycle [v6]

[Denghui Dong]

> Hi,
> 
> Could I have a review of this change that merges three vm operations(VM_PrintThreads, VM_PrintJNI, VM_FindDeadlocks) in thread_dump and signal_thread_entry.
> 
> `jstack` is a very common command, even in the production environment.
> 
> In addition to reduce the cost of entering safepoint, I think this patch also could ensure the consistency of the results of VM_PrintThreads and VM_FindDeadlocks.

Denghui Dong has updated the pull request incrementally with one additional commit since the last revision:

  update according to the comments

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4504/files
  - new: https://git.openjdk.java.net/jdk/pull/4504/files/bec65ddb..c9a65726

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4504&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4504&range=04-05

  Stats: 10 lines in 6 files changed: 0 ins; 1 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4504.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4504/head:pull/4504

PR: https://git.openjdk.java.net/jdk/pull/4504