Bug 1868737 - Allow minimal gfx features by default for uncertain...

Bug 1868737 - Allow minimal gfx features by default for uncertain configurations. r=jrmuizel,perftest-reviewers,kshampur a=RyanVM

Some features such as the GPU process (except on Android), backdrop
filter (because it always works with Software WebRender), ANGLE (because
it is generally good) and out of process WebGL (we generally want to
remote WebGL for sandboxing purposes) are special, and should not be
disabled simply because we are uncertain about our configuration. In
these situations, disable most features, but keep these enabled by
default.