~10% or more Linux users* do not have AMD/ATI in the GL_VENDOR,
only in GL_RENDERER. Our heuristics only checked GL_VENDOR, so
this CL adds GL_RENDERER to the string being checked to find the
vendor ID.
(*According to https://feedback.wildfiregames.com/report/opengl/feature/GL_VENDOR)

Bug: angleproject:4204
Change-Id: Ie89080b4431fdf02a4ca09709973ea3f271a3e84
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1953486Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>