[JDK21] Support JvmtiMountTransition Annotation

[babsingh]

JvmtiMountTransition annotation's description:

• A method is annotated as "jvmti mount transition" if it starts or ends virtual thread mount state transition (VTMS transition).
• This annotation is only used for VirtualThread methods, which are skipped during JVMTI inspection.

[thallium]

#16654 implements check for method entry and method exit events. Not sure if that suffices.

[babsingh]

#16654 implements check for method entry and method exit events. Not sure if that suffices.

No, #16654 only disables certain JVMTI events; it does not hide/skip method frames with the JvmtiMountTransition annotation. At some places, the RI skips the method frames with the JvmtiMountTransition annotation while stackwalking in the JVMTI. MethodExitTest, which is currently disabled, utilizes the hide frame feature. Related: #17490.

[babsingh]

Work done to support the JvmtiMountTransition annotation:

• Implement JVM_VirtualThreadHideFrames() #16654
• Skip methods with JvmtiMountTransition annotation in findDecompileInfo #17855

Pending task from #17855 (comment):

There are stack trace APIs in JVMTI - the depth of frames will now not match (i.e. get a stack trace, find a method at depth 3, then try to use one of the APIs modified here, and fail because the deoth is off due to an annotated method).

Yes. We will need to apply this change to all places where walkStackFrames is used in JVMTI functions. Will address this in a follow up PR.