Add a stub for NativeMethodHandle in JDK16

[babsingh]

fixes: #11255

Signed-off-by: Babneet Singh sbabneet@ca.ibm.com

[babsingh]

I tried to turn-on the opt_panama and Panama (JCL) flags in order to enable the OpenJ9 NativeMethodHandle support. But, I ended up facing many issues:

1. jdk.internal.nicl and java.nicl packages no longer exist in JDK16. Finding their new equivalent representation will take some time.
2. MethodHandles class no longer has the findNative* methods.
3. Library class is no longer available; potentially renamed to NativeLibrary and relocated.
4. gcc error: Jit.hpp in JavaMethodCallbackGen.cpp cannot be found.
5. ... the list goes on

The above conflicts cannot be resolved quickly. So, I have added a minimal stub for the NativeMethodHandle class, which should allow us to quickly enable JDK16 builds.

[babsingh]

Suggested PR builds:

Jenkins test sanity xlinux jdk11
Jenkins test sanity xlinux jdknext
Jenkins test zlinux jdknext depends ibmruntimes/openj9-openjdk-jdk#openj9-staging

All builds should pass. The jdknext openj9 build will fail because the NativeEntryPoint class only exists in the jdknext openj9-staging branch at this point.

[babsingh]

fyi @tajila @JasonFengJ9 @pshipton @gacholio @keithc-ca

[tajila]

Jenkins test sanity xlinux jdk11

[tajila]

Jenkins test sanity plinux jdknext

[tajila]

Jenkins test sanity zlinux jdknext depends ibmruntimes/openj9-openjdk-jdk#openj9-staging

[babsingh]

All the recent feedback has been addressed. Unfortunately, the jdknext openj9 build will be unsuccessful since NativeEntryPoint only exists in jdknext openj9-staging at this point.

[keithc-ca]

Jenkins test sanity xlinux jdk11

[keithc-ca]

Jenkins test sanity zlinux jdknext depends ibmruntimes/openj9-openjdk-jdk#openj9-staging