Migrate from Azure Pipelines to Github Actions (#474)

This commit migrates wasmtime's CI infrastructure from Azure Pipelines
to Github Actions. Using Github Actions has a few benefits over other
offerings:

* Being natively integrated with Github means that there's no degree of
  user account configuration or access control management, it's all
  inherent via already existing Github permissions.

* Github Actions gives 20 parallel builders instead of Azure's 10 by
  default, which is a nice boost to have!

Overall I've found Github Actions to feel a bit cleaner than Azure
Pipelines as well. Subjectively I've found the configuration to be more
readable and more pleasant to work with, although they're both just as
"powerful" I think. Additionally Github Actions has been pretty solid in
my own personal testing for a number of other projects.

The main trickiness with wasmtime's CI is the rolling `dev` release of
the master branch as well as binary releases for tags. Github Actions
doesn't have quite as much built in functionality as Azure Pipelines,
but Github Actions does have a nice feature where you can define the
code for an action locally rather than only using built-in actions.

This migration adds three local actions with some associated JS code to
run the action (currently it looks like it basically requires JS)

* An `install-rust` action papers over the gotchas about installing
  Rust, allowing Rust installation to be a one-liner in the configuration.

* A `binary-compatible-builds` action allows easily configuring the
  wheels and the binaries to be "more binary compatible" and handles
  things like compilation flags on OSX and Windows while handling the
  `centos:6` container on Linux.

* The `github-release` action is the logic using the `@actions/github`
  JS package to orchestrate the custom way we manage rolling releases,
  ensuring that a new release is made for the master branch under `dev`
  (deleting the previous tag/release ahead of time) and then also
  manages tagged releases by uploading them there.

I'm hoping that most of the inline actions here will largely go away.
For example `install-rust` should be simply `rustup update $toolchain`
once various environment issues are fixed on Github Actions runner
images. Additionally `github-release` will ideally migrate to something
like https://github.com/actions/create-release or similar once it has
enough functionality. I'm also hoping that the maintenance in the
meantime of these actions is pretty low-cost, but if it becomes an issue
we can look into other solutions!

.github/actions/github-release/main.js

@@ -0,0 +1,91 @@
+const core = require('@actions/core');
+const path = require("path");
+const fs = require("fs");
+const github = require('@actions/github');
+const glob = require('glob');
+
+async function run() {
+  // Load all our inputs and env vars. Note that `getInput` reads from `INPUT_*`
+  const files = core.getInput('files');
+  const name = core.getInput('name');
+  const token = core.getInput('token');
+  const slug = process.env.GITHUB_REPOSITORY;
+  const owner = slug.split('/')[0];
+  const repo = slug.split('/')[1];
+  const sha = process.env.GITHUB_SHA;
+
+  core.info(`files: ${files}`);
+  core.info(`name: ${name}`);
+  core.info(`token: ${token}`);
+
+  const octokit = new github.GitHub(token);
+
+  // If this is a `dev` release then we need to actually delete the previous
+  // release since we can't overwrite a new one. We also need to update the
+  // `dev` tag while we're at it. So here you'll see:
+  //
+  // * Look for the `dev` release, then delete it if it exists
+  // * Update the `dev` release to our current sha, or create one if it doesn't
+  //   exist
+  if (name == 'dev') {
+    const releases = await octokit.paginate("GET /repos/:owner/:repo/releases", { owner, repo });
+    for (const release of releases) {
+      if (release.tag_name !== 'dev') {
+        continue;
+      }
+      const release_id = release.id;
+      core.info(`deleting release ${release_id}`);
+      await octokit.repos.deleteRelease({ owner, repo, release_id });
+    }
+
+    try {
+      core.info(`updating dev tag`);
+      await octokit.git.updateRef({
+          owner,
+          repo,
+          ref: 'tags/dev',
+          sha,
+          force: true,
+      });
+    } catch (e) {
+      console.log("ERROR: ", JSON.stringify(e, null, 2));
+      core.info(`creating dev tag`);
+      await octokit.git.createTag({
+        owner,
+        repo,
+        tag: 'dev',
+        message: 'dev release',
+        object: sha,
+        type: 'commit',
+      });
+    }
+  }
+
+  // Creates an official GitHub release for this `tag`, and if this is `dev`
+  // then we know that from the previous block this should be a fresh release.
+  core.info(`creating a release`);
+  const release = await octokit.repos.createRelease({
+    owner,
+    repo,
+    tag_name: name,
+    prerelease: name === 'dev',
+  });
+
+  // Upload all the relevant assets for this release as just general blobs.
+  for (const file of glob.sync(files)) {
+    const size = fs.statSync(file).size;
+    core.info(`upload ${file}`);
+    await octokit.repos.uploadReleaseAsset({
+      file: fs.createReadStream(file),
+      headers: { 'content-length': size, 'content-type': 'application/octet-stream' },
+      name: path.basename(file),
+      url: release.data.upload_url,
+    })
+  }
+}
+
+run().catch(err => {
+  console.log("ERROR: ", JSON.stringify(err, null, 2));
+  core.setFailed(err.message);
+  console.log(err.stack);
+});