Fix WPT sync and simplify the update scripts (#29999)

Much of the code used to import WPT tests from upstream has been moved
to the WPT repository itself, so this can be reused. In addition,
simplify the workflows by merging the entire process into mach and also
directly into the GitHub workflow. This should fix WPT imports after
combining compilation of layout and legacy layout.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

.github/workflows/linux-wpt.yml

@@ -41,10 +41,10 @@ jobs:
           wget http://mirrors.kernel.org/ubuntu/pool/main/libf/libffi/libffi6_3.2.1-8_amd64.deb
           sudo apt install ./libffi6_3.2.1-8_amd64.deb
           python3 ./mach bootstrap-gstreamer
-      - name: Fetch upstream changes before testing
+      - name: Sync from upstream WPT
         if: ${{ inputs.wpt == 'sync' }}
         run: |
-          ./etc/ci/update-wpt-checkout fetch-upstream-changes
+          ./mach update-wpt --sync --patch
       - name: Run tests
         if: ${{ inputs.wpt != 'sync' }}
         run: |