Add option to disable super-slow "Proof View Diff"

[Blaisorblade]

• Some initial testing confirms @4ever2's diagnosis in Issues with speed/output of goal display (1s in CoqIDE, 3min in VSCoq) #317 (comment).
• Apologies if this is unfinished; this was a quick prototype, but it's already robust enough that one can enable and disable the option and see the effect immediately. And I know I don't really know TypeScript well.
• If I actually knew TypeScript, I'd maybe try using SettingsState.proofViewDiff? instead of adding a new boolean.

Initial testcase

Adapted from #317 (comment) with size 500 (I didn't want to wait for 3 minutes).

Require Import ZArith.
Open Scope Z.

Goal forall x, x>=500.
intros x.
Time cbv.

[TheoWinterhalter]

I have a silly question: with your patch, can you still get proof diff but from Coq (which is faster if I understood correctly) or will this require yet another patch?

[Blaisorblade]

@TheoWinterhalter it would need another patch, but I feel "VsCoq stops hanging for minutes" is still valuable, and a low-hanging fruit. The existing diffs still work AFAICT, and you can even tweak the setting without reloading the file.

[thery]

Can we merge?

[Blaisorblade]

Assuming the bump hasn't changed things, this should be pretty safe and keep the old behavior by default. (Maybe we should change the default).

[Blaisorblade]

Thanks for merging!