RFR: 8258754: Gracefully fallback to the OpenGL rendering pipeline if Metal rendering pipeline initialization fails [v2]

[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 incrementally with one additional commit since the last revision:

  do metal framework availability check once and cache it

-------------

Changes:
  - all: https://git.openjdk.java.net/lanai/pull/147/files
  - new: https://git.openjdk.java.net/lanai/pull/147/files/e752955c..b4bfed4b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=lanai&pr=147&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=lanai&pr=147&range=00-01

  Stats: 44 lines in 3 files changed: 31 ins; 5 del; 8 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