Merge #2151

2151: Resolve (and complete) trait calls like `Vec::default()` r=flodiebold a=flodiebold

Similar to rustc, we do this using the same code as the method call resolution, just without doing autoderef (and considering more potential candidates).

(Btw, we currently don't complete methods with `self` in path notation, even though they'd be legal to use, so maybe we should -- on the other hand, that will usually not be the most interesting completions...)

Co-authored-by: Florian Diebold <flodiebold@gmail.com>