Since strip_later is doing a good job stripping laters in the conclusion,
these tactics are thus no longer needed. Also, wp_finish now properly
converts the result in a primitive viewshift in case it is not a weakestpre.

And introduce more useful variants with a wand.

and show that this is an instance of evaluation contexts

This seems to shorten type class search.

Just because we don't have such comments for other files, doesn't mean we can't
start applying some best practices.

This required a new ectx axiom: Positivity of evaluation contexts. This axiom was
also present in the old Iris 1.1 development, back when it still derived lifting
axioms for ectx languages.

Also remove some superfluous map_ prefixes.