Build on and for Windows on Taskcluster CI
I’ve configured a `servo-win2016` Taskcluster worker type and built an AMI for it. The docs and scripts for this are in `etc/taskcluster/windows` in this PR. They don’t strictly need to be in this repository, but it’s as good a place as any.
This PR also adds a new Windows task similar to Buildbot’s `windows-msvc-dev` job. Like the other tasks triggered on `github-push` events (in particular pushes by Homu to the `auto`), it needs to succeed for a PR to be merged.
CC https://github.com/servo/saltfs/issues/559
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Upgrade mozjs.
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#21469
- [x] There are tests for these changes
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Rewrite Taskcluster integration
This rewrites this repository’s integration with Taskcluster to have a decision task that runs an in-tree Python script to schedule a graph of other tasks with inter-dependencies, saved build artifacts, Docker images built from in-tree `Dockerfile`s, etc. This also adds support fail daily tasks, run automatically every 24 hours. See `etc/ci/taskcluster/README.md` for more details.
Example of a green build with web-platform-tests enabled: https://tools.taskcluster.net/groups/aDL0pUBkSmuhezT1OF80_g
For now this PR only enables one task, equivalent to Buildbot’s `linux-dev` job. (Running Tidy and other linting tools, compiling in debug mode, and running unit tests.) At this time Homu does **not** yet block PRs from merging on a successful result from Taskcluster, but I plan to do this soon after this PR lands.
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