Revert "Remove overall vcpkg cache of all installed packages"

This reverts commit b436350.

It appears there is a significant speed advantage to caching all packages as a whole.

.github/workflows/build.yml

@@ -30,6 +30,13 @@ jobs:
           core.exportVariable('ACTIONS_CACHE_URL', process.env.ACTIONS_CACHE_URL || '');
           core.exportVariable('ACTIONS_RUNTIME_TOKEN', process.env.ACTIONS_RUNTIME_TOKEN || '');
 
+    - name: Restore vcpkg dependency cache
+      uses: actions/cache@v4
+      id: cache
+      with:
+        path: vcpkg_installed
+        key: ${{ runner.os }}-${{ matrix.platform }}-${{ hashFiles('vcpkg.json') }}
+
     - name: Restore incremental build cache
       uses: actions/cache/restore@v4
       if: github.ref != format('refs/heads/{0}', github.event.repository.default_branch)