swift234

[Type checker] Use call argument matching even with type variables on the left-hand side.

Rather than using a specialized matching rule in the type checker that
depends on having default arguments in types, use call argument
matching consistently.

Note #1: This (correctly) breaks some existing code that depends on
inferring a parameter type of () for a single-argument parameter from
a no-argument function type().

Note #2: This pessimizes a code completion test, where the code
completion engine seems to depend on some quirks of argument
matching. The "type relationship" matching needs non-trivial work.