RFR: 8284378: Make Metal the default Java 2D rendering pipeline for macOS

[Ajit Ghaisas]

This PR makes Metal rendering pipeline as the default Java 2D rendering pipeline for macOS.

Please refer "JBS Description" for more details.

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Commit messages:
 - Make Metal the default 2D pipeline

Changes: https://git.openjdk.java.net/jdk/pull/8121/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8121&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284378
  Stats: 5 lines in 1 file changed: 0 ins; 1 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8121.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8121/head:pull/8121

PR: https://git.openjdk.java.net/jdk/pull/8121