Previously this function would just count bytes which was very easily
broken by incantations like `Ő̶̧͍̹͔̮̮̦͌̈̌̂́̊͜K͖̮̼̯͖͆͋̓̀̕` which take up 52 bytes while being just
2 normal width characters visually.
`terminal_display_width` correctly counts `Ő̶̧͍̹͔̮̮̦͌̈̌̂́̊͜K͖̮̼̯͖͆͋̓̀̕` as 2 visual characters.
Note: GitHub strips all these in their web UI but there are many Unicode
combining characters after each letter of the `OK`s above that produce
a "cursed" text effect.
Fixes#17772