Install visionOS simulator and switch quickstart to Xcode 16.4

Author: andrewheard

.github/workflows/common.yml

@@ -106,8 +106,8 @@ jobs:
       run: sudo xcode-select -s /Applications/${{ matrix.xcode }}.app/Contents/Developer
     - name: Install visionOS, if needed.
       if: matrix.platform == 'visionOS'
-      run: ls $(xcode-select -p)/Platforms/XROS.platform || \
-        { xcodebuild -downloadPlatform visionOS }
+      run:
+        xcodebuild -downloadPlatform visionOS
     - name: Run setup command, if needed.
       if: inputs.setup_command != ''
       run: ${{ inputs.setup_command }}

.github/workflows/firebaseai.yml

@@ -86,7 +86,7 @@ jobs:
       matrix:
         include:
           - os: macos-15
-            xcode: Xcode_16.2
+            xcode: Xcode_16.4
     runs-on: ${{ matrix.os }}
     env:
       BRANCH_NAME: ${{ github.head_ref || github.ref_name || 'main' }}