Ensure cached directory exists before restoring

Fix for #25

Use @action/cache v2.0 for faster caching

• remove actions/cache as a subrepo;
• use @actions/cache v2.0 npm package;
• faster de-compress with zstd;

Insert actions/cache v1.2

To automatically cache/restore vcpkg along with its artifacts, the run-vcpkg action is now using actions/cache v1.2 which brings bug fixes and improvements.

Add overlay support

Ensure --overlay-ports= is passed to all vcpkg invocations.

Auto cache of vcpkg and its artifacts

No need to use actions/cache, the run-vcpkg action does it for you.

Add setupOnly mode, add shell support

Added input setupOnly to install and setup vcpkg without installing any ports. Leveraging $VCPKG_ROOT (or the step output RUNVCPKG_VCPKG_ROOT_OUT) it is then possible to use it in a subsequent run steps.
Added input useShell, true by default, it allows to access to shell features like environment variables.

The multi-platform run-vcpkg action

Build dependencies for C/C++ source code on GitHub workflows using the multi-platform run-vcpkg GitHub action.