Deprecate `--no-binary` disabling the wheel cache

[sbidoul]

Currently, --no-binary disables reading the wheel cache.

The wheel cache is however populated in some cases (such as when using pip wheel --no-binary or pip install --no-binary for projects with a pyproject.toml.

We want --no-binary to mean only one thing, namely "don't download wheels".

So we deprecate this behaviour and add a no-binary-enable-wheel-cache feature flag that will become the default in the future.

The recommended alternative is to use --no-cache or separate cache directories using --no-cache-dir.