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/lint.yml

@@ -31,9 +31,8 @@ jobs:
         uses: mozilla-actions/sccache-action@v0.0.6
       - name: Set LIBCLANG_PATH env # needed for bindgen in mozangle
         run: echo "LIBCLANG_PATH=/usr/lib/llvm-14/lib" >> $GITHUB_ENV
-      - uses: actions/setup-python@v5
-        with:
-          python-version: '3.10'
+      - name: Setup Python
+        uses: ./.github/actions/setup-python
       - name: Install taplo
         uses: baptiste0928/cargo-install@v3
         with:
@@ -46,8 +45,6 @@ jobs:
           locked: true
           # 0.16.2 requires Rust 1.81 or newer.
           version: '0.16.1'
-      - name: Bootstrap Python
-        run: python3 -m pip install --upgrade pip
       - name: Bootstrap dependencies
         run: |
           sudo apt update
@@ -57,4 +54,4 @@ jobs:
         run: |
           python3 ./mach clippy --use-crown --locked -- -- --deny warnings
       - name: Tidy
-        run: python3 ./mach test-tidy --no-progress --all
+        run: python3 ./mach test-tidy --no-progress --all