t: fix Lexer line count for $() inside double-quoted strings

t: fix Lexer line count for $() inside double-quoted strings

scan_dqstring's post-loop newline counter re-counts newlines that
were already counted during recursive parsing of $() bodies.  This
happens because scan_dollar returns text containing newlines (from
multi-line command substitutions), and the catch-all counter at the
end of scan_dqstring counts all of them again.

Fix this by counting newlines inline as non-special characters are
consumed, and removing the post-loop catch-all.  Each newline is
now counted exactly once: literal newlines at the inline match,
line splices at the backslash handler, and $() newlines by
scan_token during the recursive parse.

This is a latent bug: any consumer that relies on token line
numbers rather than byte offsets would get incorrect results for
tokens following a multi-line $() inside a double-quoted string.
chainlint is not affected because it annotates the original body
text using byte offsets, not token line numbers.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>