Implement missing members suggestion shadows type parameters

[zeramorphic]

In the following minimal example in latest nightly (using a struct<T> DiagnosticResult { ... }), the "implement missing members" intention shadows the type parameter T. This creates rather confusing error messages if you didn't actually read the code that it inserted! The two type parameters T and T are different, but I imagine that in a more complex scenario than this, it could hide the source of bugs. I think rust-analyzer should probably output code similar to

[Natural-selection1]

Yes, we did not check for possible duplicate names, but this will be fixed in https://github.com/rust-lang/rust-analyzer/pull/21118.