Initial OpenCL + OpenGL Nbody Demo

[grfrost]

This is just a proposed OpenCL + OpenGL Nbody demo

Uses jextract to extract Java bindings for both OpenGL and OpenCL.

Uses OpenCL for the physics and OpenGL to render.

Can compare OpenCL vs Java Multithreaded vs Java SingleThreaded

I have only tested on MacOSX so far.

The two Helpers CLWrap and GLWrap separate the jextract bindings from the NBody detail.

Both/Either can be used to create other OpenGL only or OpenCL only demos.

---

Progress

• [ ] Change must not contain extraneous whitespace
• [x] Change must be properly reviewed (no review required)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jextract.git pull/248/head:pull/248
$ git checkout pull/248

Update a local copy of the PR:
$ git checkout pull/248
$ git pull https://git.openjdk.org/jextract.git pull/248/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 248

View PR using the GUI difftool:
$ git pr show -t 248

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jextract/pull/248.diff