This gets rid of the (ambiguous) notation %l, because we can declare
LitLoc as a coercion. It also shortens the code.

FDor editors that display 0-width space with more than 0 width, this makes the indentation of assertions more consistent

That way, we do not have useless type annotations of the form
"v : language.val heap_lang" cluttering about any goal.

Note, that we could decide to eta expand everywhere (as we do for ∀
and ∃), and use the notation "WP e {{ Q }}" for "wp e ⊤ (λ _, Q)".

newline before the first context" and "shuffle 0-width spaces around so
they are distributed more evenly"

This reverts commits e3c56f9e and
7fc1124c, which are workarounds for
Coq bug https://coq.inria.fr/bugs/show_bug.cgi?id=4675

Also, this commit fixes the levels to avoid parantheses.

Pros:
* It does not matter how editors render the 0-width space, everything is always aligned
* In ProofGeneral, there is no more incorrectn indentation of the first line

Cons:
* There is an empty line between the bar ending the Coq context, and the first Iris hypothesis