Add confirm-short-comments feature - #4141

(Second attempt, after #4123)

Closes #3911

Test URLs

Any new/existing issue page: e.g.
https://github.com/sindresorhus/refined-github/issues/new
#3911

Screenshot

Currently I'm getting these 3 TypeScript errors in VSCode, which I'm unable to fix. (screenshot)
(I have run npm run lint and npm run fix).

• Property 'value' does not exist on type 'Element'. (line 10)
• Argument of type 'Element | null' is not assignable to parameter of type 'HTMLTextAreaElement | HTMLInputElement'.
  Type 'null' is not assignable to type 'HTMLTextAreaElement | HTMLInputElement'. (line 12)
• Generic type 'Event' requires between 0 and 2 type arguments. (line 17)

 
In the New Issue page it seems to be working ok.

In an existing issue page I'm having these problems:

• If I block a submission once, then I can only submit by clicking Submit (the submit shortcut Ctrl+Enter doesn't work anymore). Additionally, sometimes I cannot submit not even via the button, unless I click somewhere away and then back in the textarea. (My use of textFieldEdit -inside the refocus() function- doesn't seem to help in this case, in constrast to the New issue page)
• after blocking a submission, the Close with comment button becomes disabled. The Comment button remains enabled.

Any help would be most welcome !