Invent "MatchAnyN" option for tab-complete.c's Matches/MatchesCS.

Invent "MatchAnyN" option for tab-complete.c's Matches/MatchesCS.

This argument matches any number (including zero) of previous words.
Use it to replace the common coding pattern

	if (HeadMatches("A", "B") && TailMatches("X", "Y"))

with

	if (Matches("A", "B", MatchAnyN, "X", "Y"))

In itself this feature doesn't do much except (arguably) make the
code slightly shorter and more readable.  However, it reduces the
number of complex if-condition patterns that have to be dealt with
in the next commits in this series.

While here, restructure the *Matches implementation functions so
that the actual work is done in functions that take a char **
array of pattern strings, and the versions taking variadic arguments
are thin wrappers around the array ones.  This simplifies the
new Matches logic considerably.  At the end of this patch series,
the array functions will be the only ones that are material to
performance, so having the variadic ones be wrappers makes sense.

Discussion: https://postgr.es/m/2208466.1720729502@sss.pgh.pa.us