Add OpenGL support to Linux viewer

Also adds a command line option (--vulkan) to choose between
Vulkan and OpenGL.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2011473003

Committed: https://skia.googlesource.com/skia/+/10b3815a11c39b154ec7b74a2af43e019b50d48c

Review-Url: https://codereview.chromium.org/2011473003
6 files changed