SkMojo: test linking Skia against the Mojo SDK

TODO: build on systems other than Linux.

Add mojo_skd to the DEPS.

Add a DM::Via called `mojo-`.

everything is hidden behind the gyp variable `skia_mojo`.
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1644043003

Review URL: https://codereview.chromium.org/1644043003
10 files changed