Multistage docker containers with RBE swiftshader support

[GMNGeoffrey]

Refactors Docker setup to enable multistage builds and fully support
Vulkan.

1. Vulkan is now supported in all our build configurations and
   IREE_VULKAN_DISABLE is set to false in all build scripts.
2. Our docker containers use multi-stage builds to reduce duplication
   and image size.
3. Directory names match image names rather than having arbitrary
   underscore/dash distinction (I kept mistyping this).

New vs old images:
https://gist.github.com/GMNGeoffrey/6ea51a6035f3eb8fac11ff4bdbd6edc0

Fixes #2651

[GMNGeoffrey]

This got a bit bigger than I expected. I was fiddling around with multistage builds and didn't really see it come together until everything worked. I can break it into smaller chunks if you'd like.

[GMNGeoffrey]

Argh rollout will actually be tricky because the image names change :-/ I think we should switch to using sha256 so we can have atomic changes and just use the tags for caching. Docker caches based on layers, so it should only be a minimal performance hit as it realizes it already has all the layers. I'll test that out in a separate PR, but please take a look at these changes in the meantime :-)

[GMNGeoffrey]

This is able to rollout now thanks to #3119. PTAL

[phoenix-meadowlark]

Is it normal to use pronouns like I, my and mine in OSS code? Probably doesn't matter much either way.

[GMNGeoffrey]

Not really specific to OSS, but the appropriate use of the first person is an old argument :-D I personally lean towards it where the alternative is some twisted passive voice or other acrobatics just to avoid the first person. I could also say "we", but I dunno maybe someone else knows how to do this (Lei?). This argument also comes up in academic papers all the time. I think avoiding the first person to seem "professional" or "formal" is a much lower priority than communicating with your reader :-P

I figure blame will usually say who the speaker is, but it usually doesn't actually matter (I wouldn't write "come ask me about this" because then someone actually has to figure out the speaker). This is a note for future devs explaining why something is the way it is and I wrote it in what felt like the most natural way. I quite frequently come across things like this where it's clearly not following what you'd expect the convention would be and I go down the rabbit hole of trying to fix it and sometimes discover the original author had a good reason for not doing so and man it would've been nice if they'd left a note. I'm happy to word it differently though :-D

/rant

[GMNGeoffrey]

Whelp good thing I manually triggered that presubmit :-D