Update Skia to use the new combined Dawn+Tint repo

Includes a manual roll of Dawn, as well as tweaks to the Tint build
overrides.

Dawn needs git in order to generate a header that has the
version of Dawn compiled in. If we use Dawn's GN rules to
build it, we need git to generate that file.

Our (now updated) Bazel rules to build Dawn do not need to
do this because we (Skia) do not use this file [1]

[1] https://dawn.googlesource.com/dawn/+/088a600b03679cd20991f145173a573ed9c03480/src/dawn/common/BUILD.gn#177

Change-Id: Id19fdbb9b53fdad2397a0044a4a314b1444faeb0
Cq-Include-Trybots: luci.skia.skia.primary:Build-Debian10-Clang-x86_64-Debug-Dawn,Build-Win-Clang-x86_64-Release-Dawn
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/528157
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed