github: add script and action for getting gltf assets (#9085)

- Script for getting models from glTF-Sample-Assets
- Add support for reading gltf models from a file.

.github/workflows/presubmit.yml

@@ -118,11 +118,12 @@ jobs:
       - uses: actions/checkout@v4.1.6
         with:
           fetch-depth: 0
+      - uses: ./.github/actions/mac-prereq
+      - uses: ./.github/actions/get-gltf-assets
+      - uses: ./.github/actions/get-mesa
+      - uses: ./.github/actions/get-vulkan-sdk      
       - id: get_commit_msg
         uses: ./.github/actions/get-commit-msg
-      - uses: ./.github/actions/mac-prereq
-      - uses: ./.github/actions/get-mesa
-      - uses: ./.github/actions/get-vulkan-sdk
       - name: Prerequisites
         run: |
           pip install tifffile numpy
@@ -132,6 +133,7 @@ jobs:
       - name: Render and compare
         id: render_compare
         run: |
+          ls ./gltf/Models
           TEST_DIR=test/renderdiff
           source ${TEST_DIR}/src/preamble.sh
           start_