mach: switch to uv for managing python venv (#34504)

This patch switches servo to use `uv` for both installing a pinned
Python version as well as installing the dependency packages using
`uv`'s pip compatible interface. It also introduces a new 'composite'
GitHub action to setup python in the different CI workflows.

There is no support for externally managed python installations and
virtual environments. These could be added in the future.

Fixes #34095

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

.github/workflows/windows.yml

@@ -114,13 +114,13 @@ jobs:
           choco install wixtoolset
           echo "C:\\Program Files (x86)\\WiX Toolset v3.11\\bin" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
       - uses: actions/setup-python@v5
-        if: ${{ ! fromJSON(needs.runner-select.outputs.is-self-hosted) }}
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
         with:
-          python-version: "3.10"
+          skip-python-setup: ${{ fromJSON(needs.runner-select.outputs.is-self-hosted) }}
       - name: Bootstrap
         if: ${{ ! fromJSON(needs.runner-select.outputs.is-self-hosted) }}
         run: |
-          python -m pip install --upgrade pip
           python mach fetch
           python mach bootstrap-gstreamer
       # For some reason WiX isn't currently on the GitHub runner path. This is a