feat(#34): calculate comment line with abusive char

[VasilevNStas]

fix #34

What

The ascii-only lint reported the wrong line number for an abusive
(non-ASCII) character sitting in a multi-line comment. This puzzle is
fixed by locating the exact source line of the character.

Why

Consider a program with a two-line comment:

# This comment is fine
# but here привет
[] > foo

The parser merges both lines into a single XMIR node:

<comment line="2">This comment is fine
but here привет</comment>

The @line attribute is not the line of the comment at all: it points
at the line where the parser seals the comment block, i.e. at the next
meta or object after it. With +spdx/+architect metas present the
comment can sit on line 1 while @line says 4. Any arithmetic on top of
@line is therefore unreliable.

How

The comment text is located inside /listing (the full source code the
parser embeds into XMIR). Each line of a comment in the listing starts
with #. The lint finds the first line of the comment there:

head = first line of the comment text (up to the first '\n')
at   = listing.indexOf("# " + head)
line = number of '\n' in listing before `at` + 1
       + number of '\n' before the abusive character in the comment text

This yields the exact source line of the character, regardless of metas.
When /listing is absent (e.g. in integration tests on already-processed
XMIR) or the comment cannot be found, the lint falls back to the old
@line behavior.

Tests

Two new tests cover both shapes:

• reportsCorrectLineInMultilineComment — abusive char on the second
  line of a two-line comment (previously reported as line 3);
• reportsCorrectLineInTheMiddle — abusive char in the middle of a
  three-line comment (previously reported as line 3).

The existing unlint-ascii-only-line.eo fixture was adjusted: it used
the old (wrong) line number in +unlint, now it matches the real line
of the comment.

Both mvn test (588 tests) and mvn clean install -Pqulice pass,
plus mvn jmh:benchmark.

[VasilevNStas]

@volodya-lombrozo plz review this
I've fixed it

[VasilevNStas]

@volodya-lombrozo plz re-review