These tactics are superfluous:
- iPure H as pat => iDestruct H as pat
- iPersistent H => iSpecialize H "!"

It is no longer triggered when posing [P ⊢ Q] with [P] an evar. This, for
example, makes sure that iApply pvs_intro works, which failed before.

Now, it bases the type the quantifier ranges over on the goal, instead
of the witness. This works better when dealing with witnesses involving
type class constraints.

- It can now also frame under later.
- Better treatment of evars, it now won't end up in loops whenever the goal
  involves sub-formulas ?P and it trying to apply all framing rules eagerly.
- It no longer delta expands while framing.
- Better clean up of True sub-formulas after a successful frame. For example,
  framing "P" in "▷ ▷ P ★ Q" yields just "Q" instead of "▷ True ★ Q" or so.

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

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

This reverts commit 3cc38ff6.

The reverted pure hypotheses and variables appear in the wrong order.