Add "strict mode" validation to the Rego API

[anderseknert]

While I think the Rego API is generally quite nice to work with, there's been more than one occasion where I've spent more time than I would have liked chasing down something unexpectedly not happening as I had anticipated... only to find out later that the option I provided had no effect due to where I set it, or that some other option would override that. Examples of this include:

• Options that are only considered when set on a prepared query, or only when not set on a prepared query
• rego.StoreReadAST having no effect if a Store has been provided
• Mistakenly setting both Input/ParsedInput (or other non-parsed vs parsed options)

It's understandable how some options depend on other settings, or won't work in certain configurations, but it would save developers a lot of time if instead of silently accepting ineffectual options, there was at least an option to have such settings fail with an error.