RFR: 8316233: VirtualThreadStart events should not be thread-filtered [v2]

[Serguei Spitsyn]

> The JVMTI VirtualThreadStart events have to follow the ThreadStart events pattern and so, should not be thread-filtered.
> The fix includes:
>  - `jvmti.xml`: remov the attribute `filtered="thread"` in the `VirtuallThreadStart` event spec
>  - `jvmtiEventController.cpp`: remove the `VTHREAD_START_BIT` from the `THREAD_FILTERED_EVENT_BITS` mask and and it to the `NEED_THREAD_LIFE_EVENTS` mask
>  - `jvmtiExport.cpp`: rearrangements in the `JvmtiExport::post_vthread_start()` function
> 
> The fix also includes a couple of minor unification tweaks:
>  - to align `JvmtiExport::post_thread_end()` with `JvmtiExport::post_vthread_end()` to have a unified check for the `JVMTI_PHASE_PRIMORDIAL`.
>  -  to rename the local variable `cur_thread` as `thread` to follow the common pattern in `JvmtiExport::post_vthread_start()` and `JvmtiExport::post_vthread_end()`
>  
>  Testing: ran mach5 tiers 1-6. All tests are passed.

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

  review: convert check for is_hidden_from_external_view check() into assert

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16019/files
  - new: https://git.openjdk.org/jdk/pull/16019/files/1b716552..46ce6453

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16019&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16019&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16019.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16019/head:pull/16019

PR: https://git.openjdk.org/jdk/pull/16019