hg: loom/loom: fix the JVMTI cur_stack_depth issue; add new test ContFramePopTest

[serguei.spitsyn at oracle.com]

Changeset: 66844d04ffba
Author:    sspitsyn
Date:      2019-04-25 10:29 -0700
URL:       http://hg.openjdk.java.net/loom/loom/rev/66844d04ffba

fix the JVMTI cur_stack_depth issue; add new test ContFramePopTest

! src/hotspot/share/runtime/continuation.cpp
+ test/hotspot/jtreg/serviceability/jvmti/ContFramePopTest/MyPackage/ContFramePopTest.java
+ test/hotspot/jtreg/serviceability/jvmti/ContFramePopTest/libContFramePopTest.cpp