[copilot] setup .github/workflows/copilot-setup-steps.yml (#1344)

Context: https://docs.github.com/en/copilot/customizing-copilot/customizing-the-development-environment-for-copilot-coding-agent

Setup `.github/workflows/copilot-setup-steps.yml`, which is a Github action
that runs (only on Ubuntu) prior to Copilot doing its work.

This makes Copilot more useful, as it has a locally cloned and built source tree
with all dependencies installed. Copilot will be able to run various commands
to achieve tasks as assigned.

Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>

Author: Copilot

.github/workflows/copilot-setup-steps.yml

@@ -0,0 +1,30 @@
+name: "Copilot Setup Steps"
+
+on: workflow_dispatch
+
+jobs:
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+    
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+      with:
+        submodules: recursive
+
+    - name: Setup .NET 9
+      uses: actions/setup-dotnet@v4
+      with:
+        dotnet-version: '9.0.x'
+
+    - name: Setup Java 17
+      uses: actions/setup-java@v4
+      with:
+        distribution: 'microsoft'
+        java-version: '17'
+
+    - name: Prepare
+      run: dotnet build -t:Prepare
+
+    - name: Build
+      run: dotnet build