This is one of a series of deprecations meant to collect feedback on the ultimate goal of always installing source distributions by first building a wheel and then installing from it.

This is made with the following changes:

• add a new feature flag --use-feature=always-install-via-wheel, that is intended to become the default and only mechanism in the future
• when --no-binary is used without the feature flag, emit a deprecation warning about the fallback to setup.py install
• when --no-binary is used with the feature flag, build a wheel from the sdist (via PEP 517 or setup.py bdist_wheel) then install it
• when --no-binary is used with the feature flag, the wheel that was built locally is cached (unless the cache is disabled)
• since --install-option, --build-option and --global-option imply --no-binary, the deprecation warning will be emitted when these options are used without the feature flag
• deprecate --install-option
• allow using --build-option in the install command, as well as in requirement.txt lines, as a transitory mechanism until the ecosystem supports PEP 517 config settings, which are meant to replace both --build-options and --global-options

Towards #8102