There were 2 functions to output argument list. Consolidate them and
consistently use it from every call like production (i.e. function call,
constructor call, enum with associated values, subscript)
* Handle completion in 'parseExprKeyPath()' instead of
'parseExprPostfixSuffix()'.
* Fix a crash for implicit type keypath. e.g. '\.path.<complete>'. (SR-8042).
* Use 'completeExprKeyPath()' callback.
* Implement completion without '.'. e.g. '\Ty.path<complete>'
* Improved handling for 'subscript' in completion.
* Improved handling for optional unwrapping in completion.
https://bugs.swift.org/browse/SR-8042
rdar://problem/41262612