RFR: 8307399: get rid of compatibility ThreadStart/ThreadEnd events for virtual threads [v2]

[Serguei Spitsyn]

> The compatible lifecycle `ThreadStart/ThreadEnd` events were added in JDK 19 to support legacy virtual thread unaware JVMTI agents which do not enable the can_support_virtual_threads capability. When this capability is enabled then the `VirtualThreadStart/VirtualThreadEnd` instead of the `ThreadStart/ThreadEnd` events are generated for virtual threads and can be managed (enabled/disabled) separately. If the the `can_support_virtual_threads` capability is disabled then the `ThreadStart/ThreadEnd` events are generated for virtual threads.
> This enhancement is to get rid of the compatible lifecycle `ThreadStart/ThreadEnd` events.
> Motivation: Performance overhead from compatible lifecycle events can be significant when a lot of virtual threads are created.
> 
> Also, there is an experimental VM flag `PostVirtualThreadCompatibleLifecycleEvents` (enabled by default).
> If it is turned on then the default compatible lifecycle `ThreadStart/ThreadEnd` events for virtual threads are generated. This VM flag has to be removed now.
> 
> Testing:
> The mach5 tiers 1-6 were submitted and passed.

Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:

  minot tweaks in the VirtualThreadStartTest

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13874/files
  - new: https://git.openjdk.org/jdk/pull/13874/files/2af76a26..c5122e4e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13874&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13874&range=00-01

  Stats: 4 lines in 2 files changed: 1 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13874.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13874/head:pull/13874

PR: https://git.openjdk.org/jdk/pull/13874