RFR: 8258754: Gracefully fallback to the OpenGL rendering pipeline if Metal rendering pipeline initialization fails

[Ajit Ghaisas]

This implements fallback to the OpenGL rendering pipeline if Metal rendering pipeline initialization fails.
I have tested this fallback on 10.15.4 by stubbing code. We need real testing on a system where Metal is not available.

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Commit messages:
 - fallback to opengl if metal initialization fails

Changes: https://git.openjdk.java.net/lanai/pull/147/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=147&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258754
  Stats: 275 lines in 14 files changed: 95 ins; 144 del; 36 mod
  Patch: https://git.openjdk.java.net/lanai/pull/147.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/147/head:pull/147

PR: https://git.openjdk.java.net/lanai/pull/147