fix: cdot parser error message range

[nomeata]

as #4527 describes there is inconsistency between by, case and
next on the one hand who, if the goal isn’t closed, put squiggly
underlines on the first line, and ., which so far only squiggled the
dot (which is a very short symbol!)

With this change the same mechanism as used by case, namely
withCaseRef, is also used for ..

There is an argument for the status quo: The . tactic is more commonly used
with further tactics on the same line, and thus there is now a higher risk that
the user might think that the first tactic is broken. But

• the same argument does apply to by and case where there was an intentional
  choice to do it this way
• consistency and
• a squiggly line just under the short . is easy to miss, so it is actually
  better to underlining more here (at least until we have a better way to
  indicate incomplete proofs, which I have hopes for)

Fixes #4527, at least most of it.

[leanprover-community-mathlib4-bot]

Mathlib CI status (docs):

• ❗ Batteries CI can not be attempted yet, as the nightly-testing-2024-06-21 tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto nightly-with-mathlib, Batteries CI should run now. (2024-06-21 14:19:54)