mach: adopt uv and avoid system python (#34632)

This allows us to use `uv` for:
1. Installing a pinned Python version
2. Installing the dependency packages using `uv`'s pip compatible interface.
4. Bootstrapping `mach` without a Python installion on the host, using `uv
   run`

This change 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, #34547

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

.github/workflows/lint.yml

@@ -33,9 +33,8 @@ 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:
         with:
           crate: cargo-deny
           locked: true
-      - 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