azure-pipelines-task: add an Azure Pipelines task

Introduce a new sub-package that is an Azure Pipelines task, that wraps
the logic from the GitHub action.

Most of the @actions/core functions have 1:1 equivalents in Azure
Pipelines, so we can easily port the action logic into an Azure task
instead.

@actions/cache doesn't have the same integration, but consumers can use
the Cache@2 task directly in their pipeline YAML instead.

Note that due to difference in the task/action definition schema, some
of the input names cannot be exactly the same. Namely the `github-token`
action input is not a valid task input, due to the '-'. We maintain a
mapping of GitHub Actions -> Azure Pipelines input names and do the
translation in our ICore implemention.

Running `npm run build` followed by `npm run package` will use `ncc` to
compile all the task code into a single index.js file, and then use the
`tfx` CLI to create a VSIX extension that can be published to the Azure
DevOps Marketplace.

Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>

Author: mjcheetham

.github/workflows/azptask-vsix.yml

@@ -0,0 +1,27 @@
+name: 'Build Azure DevOps Extension'
+on:
+  pull_request:
+  push:
+    tags:
+      - 'v[0-9]*'
+    branches:
+      - main
+      - 'v[0-9]*'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v5
+      - run: cd azure-pipelines-task
+      - run: npm ci
+      - run: npm run build
+      - run: npm run lint
+      - run: npm run format && git diff-files
+      - run: npm run test
+      - run: npm run package
+      - uses: actions/upload-artifact@v4
+        with:
+          name: vsix
+          path: ./vsix/*.vsix

azure-pipelines-task/.gitignore

@@ -0,0 +1,2 @@
+lib
+vsix