move the reduction control of the proofmode to its own file and tweak it

See merge request FP/iris-coq!150

Typeclass to overload WP notation.

See merge request FP/iris-coq!146

* move PROP-envs definitions to environments.v so that we can control them without pulling in coq_tactics
* use reduction-controlled `pm_default` for proofmode accessors

Shorten proofmode error messages and test them

See merge request FP/iris-coq!156

different approach to monPred framing

See merge request FP/iris-coq!157

This should help speed up our CI by putting fewer jobs on fp-timing

Slightly weaker WP (i.e., easier to prove), so that we have an fupd where we did not

See merge request FP/iris-coq!153

make the way iMod solves side-conditions consistent with iInv

See merge request FP/iris-coq!155