RFR: 8258754: Gracefully fallback to the OpenGL rendering pipeline if Metal rendering pipeline initialization fails [v3]

[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.

Ajit Ghaisas has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge
 - do metal framework availability check once and cache it
 - fallback to opengl if metal initialization fails

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Changes: https://git.openjdk.java.net/lanai/pull/147/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=147&range=02
  Stats: 302 lines in 15 files changed: 121 ins; 143 del; 38 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