Merge #5270

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>

crates/ra_ide/src/diagnostics.rs

@@ -99,14 +99,6 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
             fix,
         })
     })
-    .on::<hir::diagnostics::MissingMatchArms, _>(|d| {
-        res.borrow_mut().push(Diagnostic {
-            range: sema.diagnostics_range(d).range,
-            message: d.message(),
-            severity: Severity::Error,
-            fix: None,
-        })
-    })
     .on::<hir::diagnostics::MissingOkInTailExpr, _>(|d| {
         let node = d.ast(db);
         let replacement = format!("Ok({})", node.syntax());