Make Metal the default Java 2D rendering pipeline for macOS

JEP 382 - macOS Metal Rendering Pipeline for Java 2D was delivered in JDK 17, but it is OFF by default, and OpenGL remains the default rendering pipeline.
Having worked through the critical issues which are specific to the Metal pipeline, and having it available in two releases of JDK already, it is time to make Metal the default pipeline.

The benefits should be that the more modern Metal API will be more stable going forward, be more power friendly, faster on most operations, and will benefit from increased focus on Metal in future Apple hardware.

It will require macOS 10.14 or later - and all systems capable of running macOS 10.14 and later automatically support metal.
To the remaining extent that JDK is supported or even functional on macOS 10.13 and earlier, they will continue to remain using OpenGL.

Reversion to OpenGL will be possible so long as it is supported by specifying -Dsun.java2d.opengl=true as a system property on the command line.