Consistently handle tab delimiters for wait event names

Consistently handle tab delimiters for wait event names

Format validation and element extraction for intermediate line
strings were inconsistent in their handling of tab delimiters,
which resulted in an unclear error when multiple tab characters
were used as a delimiter.  This fixes it by using captures from
the validation regex instead of a separate split() to avoid the
inconsistency.  Also, it ensures that \t+ is used consistently
when inspecting the strings.

Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/20250729.135638.1148639539103758555.horikyota.ntt@gmail.com