chore: Added GH Action xcodebuild-Demo.yml

* Created GitHub Action `xcodebuild-Demo.yml` from Swift template.
* Added `on.workflow_call.secrets` section with declarations for:  
	⁃ `MAPBOX_SECRET_TOKEN`  
	⁃ `MAPBOX_ACCESS_TOKEN`  
	⁃ `XWEATHER_CLIENT_ID`  
	⁃ `XWEATHER_CLIENT_SECRET`
* Added “Setup Tokens” step after checkout to use secrets to configure `~/.netrc` (for `MAPBOX_SECRET_TOKEN`) and `./Demo/AccessKeys.plist` for everything else.
* Changed “Build” step to also build for platform iOS Simulator.  
	‣ In the future, it would be good to run UI/unit tests here, to ensure the app can launch & run.

.github/workflows/xcodebuild-Demo.yml

@@ -0,0 +1,55 @@
+# This workflow will build a Swift project
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-swift
+
+name: Swift
+
+on:
+  workflow_call:
+    secrets:
+      MAPBOX_SECRET_TOKEN:
+        required: true
+      MAPBOX_ACCESS_TOKEN:
+        required: true
+      XWEATHER_CLIENT_ID:
+        required: true
+      XWEATHER_CLIENT_SECRET:
+        required: true
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+
+jobs:
+  build:
+
+    runs-on: macos-latest
+
+    steps:
+    - name: Checkout Repository
+      uses: actions/checkout@v4
+
+    - name: Setup Tokens
+      run: |
+        echo "machine api.mapbox.com login mapbox password ${{ secrets.MAPBOX_SECRET_TOKEN }}" >> ~/.netrc
+        chmod 0600 ~/.netrc
+        
+        pushd ./Demo
+        cp ./AccessKeys-Sample.plist ./AccessKeys.plist
+        defaults write "$(realpath ./AccessKeys.plist)" 'MapboxAccessToken' -string "${{ secrets.MAPBOX_ACCESS_TOKEN }}"
+        defaults write "$(realpath ./AccessKeys.plist)" 'XweatherClientID' -string "${{ secrets.XWEATHER_CLIENT_ID }}"
+        defaults write "$(realpath ./AccessKeys.plist)" 'XweatherClientSecret' -string "${{ secrets.XWEATHER_CLIENT_SECRET }}"
+        popd
+      
+    - name: Build for iOS
+      run: |
+        xcodebuild build \
+          -project ./Demo.xcodeproj \
+          -scheme 'Demo' \
+          -destination 'generic/platform=iOS'
+      
+    - name: Build for iOS Simulator
+      run: |
+        xcodebuild build \
+          -project ./Demo.xcodeproj \
+          -scheme 'Demo' \
+          -destination 'generic/platform=iOS Simulator'