unfolded logically atomic triple

The definition is a bit funky now to hack together something fast. See demo section for an example of application.

cc @dreyer @jung @robbertkrebbers @jjourdan 

See merge request !7

This is allowed as long as one of the conjuncts is thrown away (i.e. is a
wildcard _ in the introduction pattern). It corresponds to the principle of
"external choice" in linear logic.

Also, since do_head_step no longer has a purpose, I have removed it
and just use a bunch of eauto hints.

This implements issue #3.

This is more consistent with CAS, which also can be used on any value.
Note that being able to (atomically) test for equality of any value and
being able to CAS on any value is not realistic. See the discussion at
https://gitlab.mpi-sws.org/FP/iris-coq/issues/26, and in particular JH
Jourdan's observation:

  I think indeed for heap_lang this is just too complicated.

  Anyway, the role of heap_lang is not to model any actual
  programming language, but rather to show that we can do proofs
  about certain programs. The fact that you can write unrealistic
  programs is not a problem, IMHO. The only thing which is important
  is that the program that we write are realistic (i.e., faithfully
  represents the algorithm we want to p

This commit is based on a commit by Zhen Zhang who generalized equality
to work on any literal (and not just integers).

Since [inG] ranges over [cmraT]s, using an [ucmraT]s results in
[ucmra_cmraR] coercions that slow down type checking.

This commit improves the compilation time of thread_local.v by 40%.

By using the global ghost maps instead of our own ones.

The previous commit is not really necesarry anymore, but my proof
for UIP of types with decidable equality is a bit more general, so
I won't revert it.

This way we get rid of the (unused) axiom eq_rect_eq reported by coqchk.

This requirement was useful in Iris 2.0: in order to ensure that ownership of
the physical state was timeless, we required the ghost CMRA to have a timeless
unit. To avoid having additional type class parameters, or having to extend the
algebraic hierarchy, we required the units of any CMRA to be timeless.

In Iris 3.0, this issue no longer applies: ownership of the physical state is
ghost ownership in the global CMRA, whose unit is always timeless.

Thanks to Jeehoon Kang for spotting this unnecessary requirement.

There is still the reals stuff, which is caused by importint Psatz (needed
for lia) and eq_rect_eq which is caused by importint Eqdep_dec.