5270: Add argument count mismatch diagnostic r=matklad a=jonas-schievink
Closes https://github.com/rust-analyzer/rust-analyzer/issues/4025.
This currently has one false positive on this line, where `max` is resolved to `Iterator::max` instead of `Ord::max`:
8aa10c00a4/crates/expect/src/lib.rs (L263)
(I have no idea why it thinks that `usize` is an `Iterator`)
TODO:
* [x] Tests
* [x] Improve diagnostic text for method calls
Co-authored-by: Jonas Schievink <jonas.schievink@ferrous-systems.com>
89c7c55995